If that trend continues however it does add one other factor to consider as to whether it will be worth it to buy now. Yes prices are high, but look at ebay and look at the prices of the last generation technology miners, they are also very high. Crazy, impossible to make your money back high. So consider, will your 3 TH miner still command that kind of price at end of its life? If it does, you can buy it, make some money with it, then sell it to fund your next gen miner tech when it becomes available. I'm guessing the time when you could make large sums of money mining are over, but if you lower your expectations and play the game right, you could still be able to make a reasonable return on investment. No guarantees of course, but it seems for right now there are plenty of people out there willing to pay ridiculous prices for last gen tech. I'm still bullish on the price of bitcoin increasing too though, so I'd pay with cash instead of bitcoin if you can and keep the bitcoin. I haven't run all the math out though, and there are so many variables it's probably impossible anyway, you still might be better off just buying bitcoin.
eBay prices don't mean anything unless they're selling, most of that stuff just sits up there waiting for suckers. Based on the difficulty increases we're seeing now I wouldn't bet on new tech being worth much after 1-2 years. I'd look at resale as a way to recoup losses, not as a part of the main profitability equation.
I'm mining Litecoins right now, profits are possible short term and the outlay on equipment (all of which is much more salable than ASICs) is less. The amount of money you have to sink into ASICs to make a profit right now is too much for me to commit to such a risky venture. I'm not saying the potential isn't there, but I'm too risk averse to try. For all we know The bottom could fall out of this tomorrow.
