They aren't useless the secure the network.
If you decide to open a bank so you pay a contractor a lot of money to build a secure vault, and then you install lots of cameras, pay for an alarm system, and hire security guards .... and then the bank never gets robbed (maybe because the security is too tight) was it a waste of resources?
this^
however to some extent the question you may be hinting at is is there either away to
[1] use that mining for something else as well
See CureCoin, and merged mining for this.
[2] alternate system,
See POS, PeerCoin, Emunie, etc
One question in relation to [1] is do you want you bank, holding your wealth really concentrating on something else as well, perhaps no. So the mining and pos does not have to make any compromises to meet any other objective, say curecoin.
In some scenes this is one of PeerCoins argument, is concentrating on store of wealth.