No! You can run regular gas. The engine will adjust to accept regular. I used regular in my '94 Eldorado with a Northstar engine and now I'm running regular in my 2005 STS. Premium is recommended for both, but regular will do just fine.
Its 20 cents more per gallon for premium, cmon. Yes it has knock sensors which can compensate for regular, though it does so by retarding timing. Which can often result in lower mpg, higher emmisions and less power. Even then many still knock. In addition very often the oil consumption on northstars is due to carbon build up this only adds to that. Buying cleaners then to compensate more often also negates the .20 cost savings.