Am I too tall to bother modifying my old trek?
If you adjust a bike to the max and its still significantly too small, you should sell the bike and get a new bike. 

There are extra long seatposts, and extra long quill stems and what not, but in all likelihood its not really worth it if the bike doesn't fit with the normal seatpost + stem; the other parts of geometry like top tube length are probably too small anyway.