I think the Gold status benefits go to the occupants of the room and not the booker, so you would still receive “entry level” benefits in your room even if your mom booked it.
You definitely want to make use of the Ambassador program to get some discounts on your fares.
Most of the Penthouse suites on Voyager are larger than the Concierge suites, which might be the biggest selling point for the three of you. We have been on two cruises in Concierge and one in a Penthouse. We found that the value of the butler is dependent on how much “use” you make of his services. The room stewards in a Concierge suite provide almost all of what we got from our butler, but then we didn’t ask for many services beyond what we had on the earlier cruises.
we have only cruises Regent so we can’t compare it to mass market cruising but I suspect the difference between your other cruises and Regent will be bigger than between categories on Regent.