I bought a cheapish bike (Nakamura) couple of years ago, and it generally serves me well. Main problem that I have is that shifting gears, especially front gears often gets out of tune. After only a couple of rides it stops being smooth, and than I soon start having real problems while trying to shift gears (e.g when I shift 1->2 it gets stuck on 1, then i push to 3, and back to 2 and then it clicks, or similar scenarios. At one point before tuning, just trying to switch to 1 meant automatic chain falling from cogs). I tried tuning it myself, and had it tuned at LBS, but results are the same.
Question is, I guess, what can I do about it? Should I buy new derailleur? Maybe cables are bad? Bike is 3x7 and all the new stuff is 3x(8, 9, 10) would buying 3x8 be a problem? What if I go nuts and spend money on entire new power-train (front/rear, cogs/dereilleurs) which would probably be only slightly less that I paid for entire bike? Would it make sense?
Also worth mentioning is that I don't ride a bike that much. In last couple of years, I've barely rode 1000km,and so far I haven't change any part on it, or done any maintenance aside from cleaning/lubing, and derailleur tuning.