Estimated "true" TH1 income for 90 days:
if difficulty will get +30% every adjust: 0.765032 BTC;
if difficulty will get +20% every adjust: 0.919727 BTC;
if difficulty will get +15% every adjust: 1.023131 BTC;
if difficulty will get +10% every adjust: 1.151170 BTC;
if difficulty will get + 5% every adjust: 1.312023 BTC;
if difficulty will get + 0% every adjust: 1.517354 BTC;
if difficulty will get - 5% every adjust: 1.784133 BTC;
if difficulty will get -10% every adjust: 2.137610 BTC;
You can also see past difficulty adjustments here.
TH1 is definitely overpiced.
Added: whoops, it just fell down to 1.11 BTC. Not overpriced anymore.
Added 2: screw it, the orderbook is empty.
It's underpriced then, unless you expect a very big jump in difficulty, when you take into account the interest from lending it.