There are a few people here in Singapore who can do excellent mods on the SD-1 (among other pedals), with prices ranging from 40 bucks to over 100+. I've seen the results and they are well worth it. I got my SD-2 (quite like the SD-1) modded and it sounds excellent.. far better than the stock SD-1/SD-2, and exactly the tone I want.
The SD-1, DS-1, etc are very popular pedals and have been experimented with quite a bit, as opposed to some exotic pedals which most people haven't come across.. you can't go wrong with your SD-1.
I've listened to the tones from Indyguitarist's mods (from their website) but you can't really tell how good it is. With the local modders, you can go to their place and play with the pedals and hear them on a nice amp, first hand.