Another type rating isn't everything. Someone who is collecting types isn't nearly as impressive as someone who has used them.

PIC time is better than SIC time, if you're collecting time. If you're after a 121 position, then 121 PIC time is better than 121 SIC time.

SIC time is about moving to a PIC position. If you're a captain now, you have to decide what's more important to you; getting more 121 PIC experience, or adding a type. Frankly, 121 PIC experience is ore useful than SIC in a different type.