An interesting trilemma...
(1) Welfarism: Only the welfare of sentient beings has intrinsic (non-instrumental) value.
(2) Fitting Attitudes: It's fitting to have non-instrumental pro-attitudes towards just those things that have non-instrumental value.
(3) Direct Appreciation of Beauty: It's fitting to directly appreciate objects of beauty -- great art, music, natural wonders, etc. (Where "direct appreciation" is a kind of non-instrumental pro-attitude.)
I take (2) to be analytic, so the question is which of (1) or (3) to give up. Both strike me as initially quite plausible, so it's not an easy choice.
Subjectivists about aesthetic value might offer a debunking explanation of why we find (3) plausible, suggesting instead that we are systematically deluded in our aesthetic experiences. We think that our experiences of beauty consist of latching on to objective properties in the world that warrant our awed response, but in fact it's just a more-or-less arbitrary matter of what clusters of sensory properties happen to push our buttons. Or so the story goes.
On the other hand, if we want to take our aesthetic experiences seriously, and trust that they are indeed warranted when they seem to be (at least some of the time), then aesthetic value would seem to provide a fairly direct counterexample to welfarism's claimed monopoly on value.
Might we reconcile welfarism with aesthetic objectivism by suggesting that objectively beautiful objects are valuable in the indirect sense that appreciative experiences of those objects are of greater value than equally pleasant experiences of less-genuinely-beautiful objects? This still fails to vindicate the pre-theoretic datum that the gushing waterfall warrants appreciation. Instead, what becomes warranted is the abstract desire to appreciate the waterfall. This seems too indirect to be fully satisfying.
So my inclination is to reject welfarism (1) instead.
One argument for welfarism draws on the intuition that all worlds lacking sentient creatures are equally (non-)valuable. The presence of phenomenal consciousness seems to be a fundamental precondition for genuine value. I'm no longer so sure of this principle, but it seems to me that we might hold on to it without thereby committing ourselves to the idea that welfare is the only thing of value.
Just as we can think that consciousness is a precondition for (normatively significant) welfare even while one's welfare itself is affected by more than just one's internal mental states, so we might hold that consciousness is a precondition for other -- e.g. aesthetic -- values.
Put more precisely, the idea here is that the waterfall itself is non-instrumentally valuable, but only conditional on its being observed / appreciated. So a world containing only the (unobserved) waterfall would not realize its value. But still the thing that warrants our pro-attitudes is the waterfall itself (assuming the condition is met), rather than just experiences of the waterfall. So attributing non-instrumental value to the object of aesthetic experiences in this way is significantly different -- and perhaps more plausible -- than attributing value (only) to the experience itself.