I haven't tried the more expensive western-style tenon saws, but the mid-range os Japanese saws are a pleasure to use.
You can achieve good results with whatever saw you choose if you put the practice in.
That's my experience too.
I became adept with various styles of Western saws some years ago after the usual learning period and quite a few bodged tenons and dovetails. A good saw (and even a poor one) can produce good to acceptable cuts once the sawyer has got the techniques sorted. Also, a cheap hardpoint panel saw or even a bow saw of the metal frame kind, are good and quick for roughly dimensioning timber - which is their intended purpose (carpentry, not fine woodwork as in cabinetmaking).
I tried a Japanese saw (a ryoba) on a whim. (Woodwork is play for me). It took just a couple of cuts to "get" the necessary technique; and the results seemed inherently "finer" than the cuts from my Western saws. Once the kerf is properly begun (no skew needing a correction) it seems much easier to saw straight faces that are very clean from the saw. I've read this so many times on the interweb and in magazines now that I feel it's probably something about the Japanese saw design that allows this, rather than some sudden sawing talent in the users.
The woodworking novices I've had in the shed for a go at making something have expressed the same opinion after a session trying out various Western and Japanese saws. Without exception they preferred the Japanese saws because "they are easier".
I don't claim that any saw design is superior per se. After all, the Western saws can (and have been for centuries) used to make perfect joints of every kind. But a Japanese saw seems to be more forgiving of those not already expert at sawing. They do seem quicker to learn. At bottom, the pull stroke helps greatly to keep the kerf straight and even. Western saw pushing provides far more opportunity to steer the blade of the saw badly. The hard/fine teeth of Japanese saws also take less work to saw back and forth; and do seem to provide a cleaner finish than Western saws of the same tpi.
Finally, Japanese saws of the mid range kind seem better value for money than the mid range Western saws of similar function. Around £40 can get you a very good ryoba (also two saws in one) but you'd need to spend around £80 to get the same quality of function in a Western saw (e.g. a Veritas). Double that if you want a rip and a cross-cut saw, provided in one saw by the ryoba. And it's easy to spend a lot more than that on a posh Western saw for no extra functional ability.
For me (and I suspect for many others) the ability of a Japanese saw to stay sharp for a long time, with a quick and inexpensive blade replacement (if ever necessary) is another advantage because it means no sharpening. Western saws of the better quality can be sharpened because they need to be, sooner than a typical Japanese saw, for the same amount of work-done. Saw sharpening is no doubt a worthy skill to learn but ........... not if you don't need it. Do you prefer lighting a coal fire every morning to warm the house or is that auto-firing of the gas boiler preferable, even if you do have to replace a gasket once a decade?
So I'll risk a fairly definite statement (for me). Because of the factors mentioned above, my answer to the OP's question of: "Are expensive tenon saws worth it?" is no - not in a market in which you can buy an inexpensive but very high-functioning Japanese saw of equivalent ability for far less money. And it has to be Japanese as the inexpensive tenon saws (typically of the hard point teeth variety) rarely give the quality of finish of a Japanese saw and are often poorly made, to the point where they function badly.
Of course, upmarket Western tenon (and other) saws are nice to have and use, so buy one if the reasons for buying are greater than, "Does it work well and cost the least to get the required degree of ability". No one needs a Skelton saw but they must be very nice indeed to have.