just to clearify, when your using a mono you don't have your unaided eye closed. that would be a lot of work to be consantly winking that eye shut.
as for depth perception, that concept is more hype than fact IMO. true, a twin tube goggle will give you more DP but a single tube unit is not bad at all for me. you just need to relax and go with it.
i'll sell you my used pvs7bravos for $2500 if you can scape together a few more bucks. i moved into a pvs14 so never use the 7's anymore.
just don't get a gen1 unit. save some more cash and get a gen2. there are some very nice gen2 mono's out there that give very good performance in all light except total darkness (no moon) and actually are as good as gen3 in lighted urban environments or full moon settings.
these work well,,
www.usnightvision.com/Night_Vision_Products.htm?PID=0000000136