I've thought of upgrading to a 10 or 11 speed mountain bike cassette on my 2004 Giant Cypress DX, if/when I convert it to a downbar.
I have not decided if it will be economically feasible though.
In addition to the 10 or 11 speed wheel and cassette (bike currently has an 8 speed freewheel) derailleur, and brifters or road bike brake levers and barend shifters, I'll have to upgrade the brakes to (high profile) cantilevers, since brifters and/or road bike brake levers are not compatible with "V" brakes.
Admittedly, I prefer canti's over "V" brakes, but it is still an added cost.