What Scotty says...
Selling an RV can be a long and frustrating process - only a few sellers move their rigs in a relatively short time, say less tan 6 months. It's probably worth a try, but don't get your hopes up too high. And don't expect to get retail book value either - most private sales go for well under NADA retail pricing.
Be aware that you have to get substantially more than the dealer will give in trade (which is wholesale book value) if you live in a state that has a sales tax. That's because most sales taxes apply only to the net difference on a trade. If you sell your Allegro privaely, you will be buying the new one for cash and pay sales tax on the entire amount, not the difference in the trade. That often amounts to several thousand dollars in tax.
We are looking at going to a larger rig ourselves and face the same dilemma you do. Will probably advertise our rig in a few places and see what happens, but am making plans on a trade rather than private sale.
By the way, if a 2002 36 foot Dolphin LX with two slides would be of interest, email me for details! ;D