Depending what you set up, determines if it is worth it for you. Just after playing around with a lot of calculators, and the rough cost of equipment these days, you would be looking at around 200 days to recoup your investment, IF you have a source of free electricity. If you do not, then you are going to be VERY tight on generating any revenue.
Now, you will in no way EVER get close to a gigahash/sec (on X11) with two video cards. Not even 10 video cards. Probably not even with 100 high-end cards....
The best bang for the buck is the GTX 750 Ti (any brand, cheap as you can get them). Those can be sometimes had for as low as $100 used/refurb, but more often are found in the $135-$175 range right now. They are very power efficient should you NOT have a source of free electricity, and will put out around 2.2 - 2.6 MHash/s each.
My 6x rig right now generates on average ~ $4-6 USD/day worth of mixed coins that I exchange to BTC (.01) to exchange to DRK. No electricity cost. My total investment is around $1000. Now, given that I had some old parts to sell my out of pocket is closer to $650-700. This puts my ROI closer to 100-150 days (at current market rates.. which is a crapshoot every day of the week). For me it's worth it because I like to learn and play with things. If I get sour on the whole experience at any point I can resell all my hardware and recoup the majority of my investment.