If you get a significant scrypt mining rig, a
multipool and
cryptsy combo will let you mine the most profitable altcoin at
multipool, then auto-cashout to
cryptsy where you can set it to autosell your altcoin deposits for BTC.
But if your rig/s can't hash fast enough for quick payouts, you'll just be left standing with handfuls of altcoin small change you can't shift fast enough to profit.
It's the most direct and immediate way I know of to consider your scrypt mining in terms of its BTC earning power.
Multipool also totals up the current total BTC value of all your mined altcoins there, and the last few days of dogecoin have been eventful enough to be worth doing this way.
Point a competant gaming PC at it and see how you do, then compare it to hashrates of the big rigs you're considering.
(I've also seen middlecoin but with no domain name, registration or detailed altcoin stats, you can't tell what's going on there as easily and it looks like it's for big scrypt hashers and botnet lords only.)