This. I guess if I wanted to travel only every 5 years I might be able to do a suite - but being a solo traveler it would be A LOT. I did splurge on Aqua Class last summer and am again this summer (I actually was going to downgrade to a solo cabin, but my sailing is now sold out other than suites) - but in Feb 2026 I'm back to a solo IV on the Beyond.
The only restaurant you can't go to as a non-suite guest is Luminae (and as a non-Aqua guest you can't go to Blu). And there's the Retreat Lounge and sundeck that are only for suites, but there is plenty of deck space and other space for everyone.
As far as spa, I don't really do the treatments (I hate the hard sell for products or other services, and I never have luck with them paying attention to NO SALES PLEASE written on my intake form) - I'll do the area that comes with Aqua occasionally. I've seen it offered as a length of cruise pass under spa on the planner, so I gather from that there are spaces for those other than Aqua guests.