Yeah, in another post I mentioned the Texas also has risk of having taken on a player in decline, partly because of his build. I think hitting in Arlington is really going to give his power numbers a boost though and I don't think his decline is necessarily locked into a steep downward slope. I have a bit more confidence in him having a few more highly productive years. .280/35/110 is very reasonable, IMO. He doesn't miss games either. Kinsler has missed large chunks of time in different seasons and he's a corner infielder so age/decline is a bigger deal defensively than it is for a corner infielder like Prince.
I do like the deal for both teams, especially when all the other moving parts are considered. I like it more for Texas though because they got a much needed power bat and they need to try and win now. Fielder will really decline at some point but he has the chance to make a bigger impact than Kinsler.