The reason I export my keys is because of this August 1st thing.
What will happen to multibit classic if bitcoin hard forks? My understanding is that (because multibit does not get updated) only one of the 2 chains will show on multibit.
This is correct. MBC (MultiBit Classic) is not likely to receive any updates. It is effectively "end of life" and no longer maintained at all.
So I need the private keys to be readable from another wallet in case a hard fork occurs.
That's fine, but MBC isn't going to magically stop running and/or not allow you to export your keys if there is a fork. You will still be able to open up MBC and export your private keys in the event of a fork. It will just not be able to deal with both chains.
Yes I know having plain text private keys is risky, but are the multibit-encrypted private keys importable to another wallet? Or should I decrypt them first according to the above instructions posted?
The encrypted keys are not importable into any other wallets that I am aware of. None of the wallets really support importing encrypted stuff. This is mostly due to there being no real standard for exporting of encrypted keys. Wallets that do this are free to encrypt in any way they like, so it is somewhat unreasonable to expect any wallet to be able to read encrypted files generated by some other app.
If you feel you "must" export your keys now, I would highly recommend that you do so using encryption. It will make it less likely that your keys get compromised should you happen to have any unknown malware on your PC. Also, as already noted, there are tools and methods available to allow you to decrypt the file should you need to access them in the event of a fork.