Found your site while helping a friend look for traces of his lost OC. Your advertising system is intriguing — expect a non-anonymized and formal letter from me within the week.
I don't remember 100%, I think it was an Anon who casually linked this site about a year back, it's been very nice to have a booru that's constantly kept up to date. There are other archives out there, but they're a ghost town as of now.
Unsure if I can link here, but there's sthgbooru from /sthg/ that maybe gets something every two or three days, as well as another abandoned booru. Danbooru also has a tag for Sonic, about 8k posts right now. There's also Tailskicksass which has a separate section for art, a lot of it being particularly dated, although there's no tags and you have to go through all the artists' works individually.