Your math is good, but good luck reserving a room with HHonors points for 10 -15K points. My experience has run more like 25-40K points using HHonors.
25,000 HHonor points roughly equals $125 room. 30,000 a $150 room per night.
What you really have to do is establish a baseline of what the HGVC point is worth. This year the Maintenance fee of a 2 bdrm at HGVC LV Hilton (Karen) is $971 including the annual club membership fee. (This of course completely leaves out the purchase price of the underlying week entirely.)
So, $971 divided by 7000 points = 14 cents a point. So, in your scenario you have 3200 points left over @ 14 cents each = $448, generating 80,000 Hhonor points. Say you got a Hilton property at 25,000 Hhonor points, that means you get three nights for about $150 a night, where as if you pay cash you could have the same night for $125 (plus tax). Many times though a room is more like 40,000 points (or more) at which point you are only getting two nights stay. It just depends on where you stay and when.
Give it a go yourself at:
http://hhonors1.hilton.com/en_US/hh/home_index.do
You also can't deposit unused points on the fly. Rather, you are to deposit that which you want to go in Hhonors a year ahead...in other words I'd need to deposit the amount of NEXT years points I'd want to use before the end of THIS year, and I can't use those HHonors points until next year. There are other scenarios where you can rescue points going unused into Hhonors points at a lower exchange rate (1:20) and for an additional fee & again this is where the flexibility adds to the complication.
What many of us do is get a VISA or MC that generates HHonor points with purchases and use that to build up our HHonors account, along with any stays for work at Hilton properties and such. Then we have a big trip planned in cities which aren't HGVC properties, we might consider bolstering our HHonors points with the conversion.
It all depends on what you are after and that will vary from person to person.