Running an under-specced node is likely to be discovered pretty quickly. There are trustworthy metrics (that go through consensus) and non-trustworthy metrics on the nodes, and DFINITY and possibly some other NPs are actively monitoring nodes for signs of poor performance.
So yeah… having low-quality nodes would be a lot of work (to fake all the metrics) and for some things even isn’t possible - such as for the trustworthy metrics, where performance of a node gets evaluated by its the peers.
I’ve been telling this and I will keep telling this no matter what others say. TEE is not a silver bullet. TEE has been broken multiple times in the past, and will be broken again, especially given sufficient financial incentive. So TEE raises the bar, nothing more and nothing less. It also severely increases the operational complexity. So that has to be carefully evaluated and taken into account.