So long non-niche market adoption! This is as asinine as owning a computer /just/ to store a wallet.dat on.
I think it's a requirement to use bitcoin with non-negligible amounts of money on a computer. It doesn't work without security, including strong confidentability and integrity of data.
You have to realize that what is secure enough now for a home computer user is very probably not sufficient. You are not going to change that by fussing around.
Think about only one aspect: To make backups possible, pre-generated keys (addresses) are stored in the wallet. If you receive some amount of money, the security of that amount depends on the security of these keys since their creation until the money is moved to another address, which can take years.
Another point: If I can copy your wallet.dat, I can probably replace your entire bitcoin client as easily. I don't need to install a key logger then - I can do directly with the money whatever I want.
Or just another trick: You use your browser to look up payment addresses. Fine. I install some add-on into your browser which once in a while replaces some addresses with one of my owns. And you just wonder why your landlord throws you out.