Up until today I was under the impression I could really pull it off, but since the diff increase today I'm having serious doubts. I'm making around 530Kh/s ... so its obvious my balance will drop considerably.
No, its not obvious. The higher difficulty means more variability, but the long-term payout should be EXACTLY the same.
My question to you all, specially to those of you who have low hashpower ... However, power bill isn't getting any cheaper, but my hashrate isn't enough anymore.
There is no such thing as "enough" hashpower.

Do you think ivesting in a couple of 280x/7950 would make it any different right now?
Yes, you will double your earnings by adding one 7950. But again, pool difficulty has no effect on payout. ROI on a 7950 is just a couple months right now.