That is so very true! I have been debating adding another to my stable just because...
Meanwhile the bikes I have are amazing to me. A 16" SteelMaster (40+ year-old) converted from crappy derailleur 5-speed to an SA 3 speed. A Dahon Classic III (27 year-old) from the frame up with new wheels, an SA 3-speed coaster hub, two Dahon Boardwalks (3 year-old) one of which was converted to a Nexus 3-speed coaster hub, the other is stock.

I would really like to have a Downtube MiniB because of the belt drive and quick fold. I constantly vacillate, driving my wife nuts, order one (for my 70th birthday next month) and then don't order one because I don't need another bike... back and forth... Sheeshhh. It's only money. Do I want to leave an inheritance of money or a stable of bikes that I got to enjoy before being found dead on the side of the road? I'm thinking bikes... maybe I'll buy two or three more.

Anyway back to the original thread topic. If you can comfortably afford the new one, buy it; and, if necessary, sell the one you like least.