The problem with coaches over 10 yo is that financing can be difficult to get or restrictive on term. The flip side is that there are a lot of potential buyers since the real high end units become affordable to a larger market segment and they start to retain value much better than new coaches.
Personally, I'm of the opinion that well kept MH's over 10 years old represent the best bang for the buck and certainly would not sell one just because it reaches that age....especially just to buy something that starts the depreciation cycle all over again. If it's in good shape and you still enjoy it, keep it and save the $$$.
Dick
2002 43' DP Beaver Marquis Emerald Cat C-12 505 HP, 1600 Tq
2003 Jeep Grand Cherokee Overland ---toad