Then, like mxlews said, there is the 'ol case switch. Because the Mini is so small, it would be ideal. Several things you could do with this. An obvious one is to get rid of the CRT. Conversion wouldn't be worth it and a 14" LCD would be much nicer looking. Check eBay for cheap options. Then you could paint the case and add your touches to it.
Anything else would probably not be worth the expense.
wow I used to have one of those. but it was the 75 mhz one. It was crappy, even in 1995! Actually It had so many problems apple switch it for a performa 6360 which was a really nice upgade. They also made my dad sign a waver agreeing that the performa switch was good enough for him not to sue them. I can't even remember the controversy, but I clearly remember the crappiness of that system