The signal quality is compromised only if you think it is compromised. In other words, if you believe you hear a change when the plates are used, then you shouldn't use the plates if the highest fidelity is your goal. However, to carry that logic to its rightful conclusion, you would also eliminate the connectors at the amp and speaker.
If you buy a cheap wall plate, there's a good chance the connectors will be of inferior construction and the materials difference through which the signal must pass would be slightly noticeable to some listeners. Yet another listener might not notice the change because they are not tuned into what is happening to the signal. If you're not listening for certain qualities, they can be grossly distorted by another listener's account and you won't hear what they detect. It's not a matter of "golden ears" but rather just your priorities vs another person's priorities.
If you're running a HT receiver, then the chances are good you will not notice anything the wall plates might contribute or subtract - the front end of the system just isn't capable of sufficient transparency to matter. If you're running very high quality separates, then I think you would do best not using wall plates. Of course, once you do install wall plates and run cable through the interior of the structure, you're pretty well stuck with that cabling and future cable changes will not be advisable.