Are you on the grass this evening sir? Since ASICs are already developed, the "malicious entity" with money to burn that you talk about, would simply go and buy a bunch of ASIC to accomplish the 51% attack. They could also do the same thing with GPUs, thus, it is neither a positive or negative to either argument.
I would argue though, that a worldwide network secured by both GPU and CPU would be the hardest to attack. Take a coin like Darkcoin for instance. I believe GPU and CPU will live together on this coin somewhat, and CPU won't be entirely crowded out. If Darkcoin fails in this regard, you can always design a coin strictly for this purpose, and leverage memory requirements + hashing functions high enough that GPU always has the advantage, but CPU miners will still be around in high enough numbers.
The obvious solution to all these problems is to just have more than one block chain, with vastly different hashing functions and memory requirements for all of them. Obviously toss some Proof of Stake systems into the mix too. Wait...that's what we already have now...it only upsets people that are highly invested in Bitcoin...so they call anything that isn't Bitcoin a trash coin.
We don't need 200 coins to exist, but we do need at least 10 with highly different attributes. I figure many proof of stake coins will also survive as virtual bank accounts. I think PPC will definitely be dethroned as top PoS coin. Cashcoin in particular has a better economic model.
we do need the fastest hardware available to protect the network, if btc network still ran on cpus. and one gouverment started to develop an asic on their own in secret, 5 antminers probably where enough to kill the network. i dont think the cpu hashrate would be much higher then a terrahash.
if you want to that now you need much more then a few smart people and a few bucks to design an asic that is capable of taking over the network.