The mistake I feel that I am seeing here is the word "noble".
In my experience with Alliance, there are only a handful of players that aspire to nobility, per se. But almost every character aspires to a title of some sort. For some that title is a noble rank, for others a military rank, for others guild titles, and for yet others things that most may not even consider a title (innkeeper, master alchemist, Chessmaster, Imperial floor sweeper).
If players aspire for a leadership position that naturally includes other players (especially lower level players), creating plot that works towards that position is a very organic way to get those players to work with lower level PCs.
-MS
P.S. - I think this also covers the point Joe S. made rather well. If you aren't limiting yourself to noble titles, there are always more titles to make up.
Absolutely. Which is why I said titling.