Yeah, really. Look back at each of the things you immediately thought of and consider exactly how often each is going to come up, and exactly what can be gained from each.

Impersonating servants to get somewhere you shouldn't be doesn't actually provide all that much benefit unless your goal is "be somewhere you aren't supposed to be that a servant would be allowed to be."
Getting free stuff by impersonating an important person doesn't necessarily work, since even important people have to pay for anything that is of much use (in a campaign goals sense), and most really important people have a retinue of people they travel about with that you don't get to disguise your friends as without something more than just this spell.
Getting out of jail by disguising yourself as a dead body doesn't actually even work, in theory, because jailers are probably going to expect prisoners attempting a variety of ploys to escape and as such will probably inspect you - at the very least, physically picking you up to carry of your "corpse" is going to result in realizing you aren't dead (feign death is the spell that makes this ploy actually likely to work, not disguise self).
Sneaking into an enemy camp alone? Not a great plan if you ask me, no matter how likely your success might be (and it's not assured since looking like Jim the Enemy doesn't entail knowing how to act like Jim the Enemy, so you might get realized as out of place even if someone doesn't realize you aren't actually Jim's unknown twin).
Disappearing into a crowd doesn't even require a disguise, so there is no significant benefit their either.
Carrying weapons where they aren't allowed is either as easy as hiding them without the spell, or is as likely to fail as hiding them without the spell because the spell doesn't prevent a pat-down search from finding your weapons - and even disguising a weapon as some non-weapon object, anywhere that is trying to actually prevent weapons being brought in will have guards physically searching for hidden weapons in objects - but they won't be hidden, they'll just obviously feel like weapons even though they look like something else because the spell doesn't hold up to physical inspection.

Scaring off enemies by appearing to be something dangerous... you mean like a warlock?

Framing someone, however, is exactly the kind of thing this spell does help with - but how often do you really need to frame some specific person, rather than just prevent your actual identity being known, which a hooded cloak or any kind of mask would accomplish?

Hmm, I don't see how that can be true. You can't put on a complex disguise in an instant, but a Warlock can turn a corner and come out looking like an entirely different person a few seconds later.

Actually benefiting from a disguise, but not also having the time to apply a mundane disguise, is not a common thing - at least not any more common than a situation where "disguise" doesn't actually need to be anything but "I walked around the corner while being followed as 'that guy in the grey cloak', and then walked back out not being followed because I am know 'some guy in a blue cape' after no more than flipping a single reversible garment."

Physical disguises are nowhere near as versatile either (you can't make yourself look thinner than you are, for example, or make yourself look clean-shaven if you actually have a full beard). Not to mention that anyone can take off your physical mask to see who you really are, where you need a high level spellcaster to remove this spell.

They don't need to be as versatile in that aspect because they are more versatile in the way of which methods of detection they are capable of fooling - i.e. you can put on a fake beard and have it feel real and fully attached if someone pulls on it a little (not for a long while, nor hard enough as to actually pull real hair free of someone's face, of course), where a beard from disguise self is intangible so trying to touch it at all reveals it as obviously fake.

Not to mention that there aren't many situations in which you are going to have your physical disguise pulled off of you that aren't also situations in which you are going to be detained and observed long enough for your disguise self spell to expire, and you being bound and/or gagged to prevent spellcasting of which you are assumed capable upon being known to be disguised by magic.

Is it useful to be able to use disguise self at will? Absolutely. More useful than any of the other options you could have chosen for an invocation? Not without the campaign being tailored to ensure exactly that. Too useful for anyone to be able to take as an invocation in any campaign ever? Definitely not.

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