Honestly its too early to tell. So far Vita is in rough shape and having a rocky start. But things like price cuts, remodels, and good software can totally change its performance.
So you might be right and you might be wrong but Im not picking a number at all yet as its very early in the consoles life. The scarier thing than hardware sales is its software performance. The few people who own Vita arent buying much software for it at all.