Wait...
Yes, just as expensive...but you don't get the headaches of top swapping. How is an L26 "trickier" than an L32? They are essentially the same exact engine minus rod strength and compression ratio...and an L26 isn't commonly top swapped? FTLULZ...plenty of '04+ cars and L26's are top swapped; research guy...research. Why wouldn't you just drop an L32 in? And even more LOL's at the GXP...you want to talk about expensive aftermarket with minimal gains and a dumb setup...then sure...go buy one.
100k miles is nothing. The longevity of these motors is simple maintence, don't drive like I do all the time...and break everything...bolt-ons, a cam/heads setup all motor...or a bolt-ons top swap isn't going to "lessen" the life of anything 3800 wise.
One single turbo > Twins anyways.
To add...you give me a budget...I'll tell you the best bang for your buck mods...PM me if you want. Or discuss it here...don't care, I'll help.