I don't know if it's worth building more rigs at this point with scrypt ASICs coming out. I'm thinking about trying to add another 1MH/s, if I can do it via PCIe risers and if the PSUs can take an extra GPU. This way I'm only paying for the GPU itself not along with every other component needed to build the entire rig. I could maybe pull this off with 3x7850s. But overall building new miners is long behind me. Whatever I have I will just continuously run until I cannot profit anymore due to electricity costs. Everything is all paid off so even hardware resale value isn't considered at this point. Just running (electricity) costs.
I'm also similar to you except instead of buying more rigs at this point, I'm just diversifying it back into the crypto market. Like right now DOGE is 100% more profitable than LTC, so it makes sense to mine DOGE, keep half, and put the other into BTC (or even just $ if I feel BTC isn't a good investment at this time).
If done right, it should be way more ROI in the end than buying more GPUs at this point with Scrypt ASICs coming in. I do the same with pretty much any new alt coin - mine, sell off half to match LTC profits, and keep the other half on the house. I'm finding a very common theme here - sell a new coin when it hits an exchange. It's too profitable at first, almost always. Take your profits and buy back more later on if you really like coin, or put it into BTC or fiat.
DOGE just happened to be an exception where I decided to keep literally all of it because I spent so little time mining it.
It all comes down to if you think the ASIC's are close or not. I believe they're not. I also have all but video cards sitting here ready to build more. I have to order another Dell server PSU or two but using small PSU's to power the main components(which I have) and maybe $60 for the server PSU's and oddball cords. Over the weekend I consolidated quite a few systems using risers so now I have like 10 slots completely unused so I plan on filling all the slots I have available and then reevaluating. When the only expense is video cards the ROI is still only like 3 weeks so I should be adding a good 3Mh or so at least.