e36 M3's have been coming down a lot in price over the past few years. I love my ti and plan on keeping it for awhile too. I recently started thinking about the power issue, and there's either: swap in a 6, rebuild then supercharge the M44, or rebuild the M44 for more hp/tq (like through Metric Mechanic). OK, sure, there are a few other options out there, the the 3 listed are the most feasible.
The ti is indeed unique and rare in it's own right. I've kind of fallen in love with the idea of keeping the little 4-banger in there. This leaves me with limited and expensive options for upgrading...oh well.
If I had the money, I'd totally look for a cheaper M3 and keep the ti too. It's not too hard to find a nice one with decent mileage...they're all over the place on bimmerforums.com. Then maybe up the road you can supercharge and have two really nasty BMWs
