Greetings.
Let me tel you about my experience and those of my friends who have also done a conversion.
I finished the conversion over a year ago. I converted in the UK (ATPLs and CPL flight test), and I added the MEIR in Spain, MCC in Germany. After finishing, it took another half a year to find an instructor job (after doing a FI rating that cost me €8000).
Here are some things that I have learned...
Not all JAA licenses are the same:
If you go to the UK, it is very expensive. Theory exams are done on paper and it takes 3 weeks or more to get your results. Flight test fees are ridiculous, plus license issue fees, license renewal fees, etc... However, they are very accommodating when it comes to accepting documents from other JAA countries. For example, once you get your license issued, you can easily add a type rating, flight instructor rating, instrument rating, class rating, etc to your license even if it was done in another country.
France is even more expensive, and they won't accept ratings done in other countries (but ironically they will accept ATPL exam passes from other countries).
Spain has relatively good prices, but everything is slow. If you pass your flight test, you might wait 3 months to get your license in the mail (during which time you can't fly because you don't get a temp license in Europe). If you go to another country and get a 777 type rating, Spain won't add it to your license since there are no 777s on the Spanish register.
I could go on and on, some countries seem to be better than others.
Also, if you want to be a flight instructor in the UK, and you do a flight instructor rating in another JAA country, you might find it hard to find employment in the UK, since the Brits have their own way of doing things. These are just examples, so where your license issued and your training done will make a difference.
Next, let me tell you about finding a job. There are definitely more low time pilots than jobs for low time pilots. Most guys who finish their ratings apply to Ryanair, as they are the main company hiring low time guys. Lots of guys who don't get hired at Ryanair seem to apply to Susiair in Indonesia, as this is their backup plan. Ryanair charges €30,000 for the type rating, and you don't get paid until you finish your safety check, which could be 6 months after getting hired.
Of the guys who I know who did a conversion recently, 1 got called up for a Ryanair interview which he will have soon (he got called six months after finishing his conversion). Another guy is still looking for a job 10 months after doing a license conversion, and another guy got hired flying light piston twins in Switzerland 5 months after doing his conversion. I got a job as an instructor as soon as I finished the JAA FI rating, but the conversion took a better part of a year, and due to various circumstances and the length of the FI course, I didn't finish the FI course until 6 months after I finished the conversion.
Now, of all my friends who got a JAA license (not conversion), most who did an instructor rating got an instructor job. One of those instructors went on to Ryanair, another went on to an Air Ambulance gig, and two went on to fly the Airbus (but one in Europe, one in the middle east). Of all the guys who didn't do the FI rating, I only know 1 who got a job so far, and he got a job in Africa on a 737-200 via a connection. One friend got an interview with Ryanair and with Susiair but was unsuccessful with both, so he went back to his old job, as he has sent out dozens of applications without success. Another guy has also sent out about 50 applications with no positive response. Another guy bought an A320 type rating and the type rating provider is having problems finding him an available A320 for him to finish his type rating. And two guys got jobs at Easyjet, but they won't start the type rating until December and then they will go into a holdpool for possibly up to 2 years until they start flying the line.
Long story short, there are some jobs, it is not completely stagnant, but it isn't the land of the plenty either.
Also, the whole license conversion is a pain. If I had stayed in the US (I'm a US citizen), my pilot career would be further along by about 2 years, but like you, that wasn't my priority.
I don't think anyone really knows what the future holds in store. With the Greek Euro crisis, slow/nonexistant economic recovery, and the closure of several major and national airlines in Europe, it currently doesn't look great. Also, for those who are putting all their eggs in the Ryanair basket, Ryanair is expected the receive the last of their deliveries soon, therefore hiring will slow most likely. Honestly though, I don't think anyone really knows what the future holds.
What I observe is that LoCos are growing (Norwegian, Ryanair, Vueling, etc...), and lots of these companies are charging for a type rating. Some companies only have one way to get hired, such as Easyjet via CTC scheme. In fact, CTC seems to hold the hiring for several UK airlines, so you mess it up with CTC and you pretty much lost your chance at half a dozen airlines.
Now, you asked about JAA/EASA transition. I don't think that there is so much of a grey area. There are some changes. Medical certification is supposedly less restrictive. Also, laws will be better harmonized. Let's look at licensing for example:
In the UK, someone with your experience requires taking the ATPL theory course plus exams, CPL flight test, and a minimum of 15 hours of IR training plus IR flight test to do a conversion.
In Switzerland, you actually wouldn't have to take the ATPL theory course but still take the exams, and the minimum 15 hours IR don't exist (15 hour IR training is a UK requirement, not a JAA requirement).
In Spain, you would have to do the ATPL theory course plus exams, the whole IR training syllabus of 55 hours, and whole CPL syllabus of 25 hours.
Under EASA, each country would supposedly have the same rules. There is a transition period and each country can take its time with the transition, but the UK is enforcing these rules starting in July. I don't really see any legislative grey area that will bite you in the rear (at least not that I see).
Ok, sorry if I rambled, your post was long so I wanted to try to cover everything. Let me know if you have more questions.