IMO, if you're talking about logging 10ish SIC safety pilot hours towards your commercial, do it. At current aircraft rental prices that can save you $1000, I find it difficult to believe that 500, 1000, 1500, etc, hours down the road some airline is going to fault you for for logging 10 hours or so of perfectly legal SIC time in a 182 to help you obtain the commercial cert. Now if you show up to an interview with a significant percentage of time as SIC in a single pilot plane that is a different story.
As for the endorsements, you will need the complex endorsement for commercial anyways. The high performance may not hurt to have down the road. If you can spare the money I would get them. You never know if you will be able to find one of these people who is willing to just let you fly them around on a couple $100 hamburger runs and log the PIC time outright.
I've logged some SIC time in single pilot planes under 135 that required an SIC, and I found it to be valuable experience. It does not comprise a significant percentage of my total time, and if airlines want to subtract it from my total time then I'm fine with that. It gave me different types of experience (actual, bad wx, icing, turbine, high alt ops) that I can't get beating the pattern with a student. If anything it made me a more well-rounded pilot and instructor. I realize the airlines frown upon it, but logging it is the only proof I have that I have this kind of experience, and its some hours that may come in handy for getting my ATP or insurance minimums for some job down the road. I would suggest to anyone that has the opportunity to get some hours as SIC for a 135 to do so. Just remember its not going to get you an airline job, and if you show up to an interview with 1000 hours and 100+ of it is SIC in a King Air 90 then that may not look so good.