It depends what you're after. My '00 650 + a barrelload of money still cost less than a good nick thou- yes, it's slower in a straight line but it's better at absolutely everything else. For me, the SV's near to the perfect bike- it's the right size, the right shape, lightweight, and it's cheap- both to buy, run and repair.
There's other elements to it... I enjoy doing the work- I wouldn't do it otherwise. I'd never take the bike to a shop and say "Make it faster".
Also, having a different bike from everyone else is a bonus for me. I'm a huge fan of the second glance- park up at a bike meeting spot or a dealership, and 9/10 I'll end up having a chat with someone about the bike.
I'd like to say insurance, but sadly my bike now costs more to insure than a standard thou
Lastly, most of the mods I've done haven't been for out-and-out power. Yes, the exhaust system and cams do ad peak power, and a fair bit of it, but mainly it gives far better rideability- more low end torque, more midrange power, better delivery, and a far wider peak.