It seems to me that for any bank or profit-driven entity that can invest significantly in Bitcoin mining, it would be better that Bitcoins appreciate as opposed to being made worthless.

Let's suppose by investing 50000 BTC (~$40M as of Jan 2014), I can get 51% of the total hashing power. This should give me 3600 BTC a day.  Sure, I would have electricity costs, but these should be a fraction, my income should be in the order of say 2000 BTC a day.

I can then recover my investment in a few months (even with accelerated complexity & cost) and the rest would be pure profit in Bitcoins.  In this case, I would prefer that Bitcoin appreciates in value and thus I get great returns with my initial investment.

Of course, it would be a different conclusion when a group (or more likely to be a group governments than corporations) decides first the Bitcoin network should be destroyed, rather than them making profit/loss decisions on the new investment.  But, in that case, we should consider that BTC network would respond to this attack in some fashion as well to protect the worth of network.