Upgrade the old - feasible? Or go w/the new?

Got an older Mac Mini w/ OS 10.4.11, 1.66 GHZ and 2 gigs of 667MHZ DDR2. Is it worth upgrading to the most modern OS compatible w/ my mini or abandoning this unit in favor of the latest i5 or i7 mini w/ its up-to-date OS and accompanying apps? This OS is archaic a far as using apps that want newer software to operate! Knew I'd have to upgrade eventually....

Thanks!

TP