Many speedcubers hit a plateau after a number of years and get bored, true, but it's a deep subject. Every solve is different and there is endless opprotunity for optimization and improvisation. And the physical dexterity aspect just adds to the fun. It would get boring only if you never improved or learned anything new. Definitely more satisfying than Sudoku or Solitaire.
If you find Sudoku boring you just need to add more constraints. For example, try solving one by considering some ordering on the entries (say, Left-to-Right then Top-to-Bottom) and only allow yourself to fill in entries in that order... then time yourself!
Sudoku is very boring. If I wanted to spend my time solving small value NP-complete problems I might as well go out and solve TSPs over and over again.
We are valuers; just because our lifetimes are finite does not mean that what we value vanishes when we die--there are children, friends, institutions, even a broader affection for the best of mankind in general, and love of justice and principle, that extend well beyond your own grave.
