My investment in lenses, though not huge, is only good stuff... 24-70...$2000 Sold to a pro last weekend 17-35...$1500 16FE....$750 I got in the islands
A few others I am keeping no matter what like my 50 1.4 and some older glass. No DX in the stable anymore though.
Will check out the 3100 specs in more detail and then fondle one next time the store. One aspect that has been fun with the E-p3 has been the use of adapters and using any glass on the thing. Makes for a fun and creative day.