Key point, I think, is that you have to have “standing” to ask a court to enforce it.
If your HOA decides, in their great officiousness, that nobody should have an outdoor dog pen, but there’s no law against it in your municipality, no neighbor has voiced a complaint about your dogs, and there’s nothing in your deed or HOA agreement that could be reasonably construed as your having ceded a right to regulate what you put in your yard to the HOA, you can tell them to go pound salt. Likewise if your busybody neighbor finds your hydrangea bush outrageously tacky, and there are no rules about plantings that are legally enforceable, she’s bsically out of luck. It needs to be something legally enforceable. You may want to act voluntarily to avoid the PITA aspects of a lawsuit on something that is legally enforceable, but the bottom line is, can X show a valid reason to take Y to court over some issue.
Now, let’s assume that there are deed restrictions, as in the OP, and that someone is violating them. Herman Blucher, inveterate tinkerer with cars, just retired and has started up Blucher’s House o’Junkers in his yard. This violates the deed restriction on unregistered cars. Do you have standing to take him to court?
The answer is, Maybe. Not yes, not no, but maybe. To have standing, you have to show that you have suffered a “legal injury”. This does not mean, you got wounded or something – but that his actions have in some way harmed you.
For example, it has lowered your property value. To prove this, you get an appraiser to tell you, in a formal letter of appraisal, what your house is worth, fair market value, (a) under the current conditions, and (b) under the assumption that Blucher’s wrecks are removed and the property kept to municipal standards. The difference in the two figures is a valid loss – what his maintaining his junkers has cost you in actual personal worth. Or you document in some way that having the junk cars there constitutes an “attractive nuisance” – presenting a danger to your children, providing a breeding ground for feral cats (which you’ve photographed), etc. You have actually shown “legal injury” from his actions, and therefore have grounds to sue.
Now of course, if you have a HOA whose job it is to seek enforcement of deed restrictions on behalf of the neighborhood as a whole, and Blucher is covered by the HOA, then complaining to them would be the way to go – they automatically would have standing, because all parties involved have previously consented, in the HOA agreement, to their having the right to enforce deed restrictions.
But that issue of standing is important. It requires that you have an objectively valid ground of complaint, something which actually has, or which has the strong potentiality to, work you a real harm. It protects against nuisance lawsuits from Mrs. Busybody, who believes that her personal tastes constitute Divine Law which all ought to follow. That’s why I included the second paragraph, putting you in the place of the person facing such a nuisance complaint.