Are there practical reasons to purchase Japanese saws to add them to my collection or are these just something I want to purchase as a gimmick?
Despite their obvious excellent qualities to be honest I think the answer is more in the realm of the gimmick/curiosity than a needed addition to the arsenal of a Western woodworker. In part this observation is based on all the fine work produced in the past by craftsmen who had never seen an Oriental saw, as well as the current work done by cabinetmakers who choose not to use Japanese saws despite their easy availability. I think this alone conclusively shows they fulfil a want, not a need.
Rob's excellent answer covers nearly all the bases on the pros and cons but I have a couple of clarifications/expansions.
Re. the thinness of kerf. It's not entirely accurate to say that Japanese saws have a thinner kerf. They tend to be much thinner than the Western saw intended for the same function — most pronounced in 'panel saws' — as due to their pull action the saw plate can be significantly thinner because it doesn't need to resist buckling when pushed against the wood. But there are some Western saws intended for cabinetry that are every bit as thin as a Japanese saw (with a shallow saw plate and stiffening spine used to resist buckling).
Re. tooth breakage, in addition to the thinness of the saw plate this is also partly down to the unusually long teeth. So even Japanese-style saws (see more on these below) with thicker blades than you would tend to see on their made-in-Japan counterparts are more prone to tooth breakage than a traditional Western saw intended for the same cut.
Related to the above point, one important aspect of Japanese saws that needs to be mentioned is that because of their historical development the tooth geometry developed largely for working on softwoods and softer hardwoods. As a result there is a strong argument against Japanese saws for woodworkers who primarily work in hardwoods, particularly in harder or tougher species. Easy-cutting species like American black walnut don't pose much of a problem, but you only have to go to other common species like oak and hard maple for a challenge to the delicate teeth on a Japanese saw. Multiply that risk manifold if working on dense tropical hardwoods. Regardless of what you use them to cut, the expression "let the tool do the work" has never been more apt.
For anyone who would like to try the mechanics of an Eastern saw without going the whole hog and buying a Japanese saw at some expense, then there are a number of Western-made saws with similar tooth geometry that cut on the pull stroke. Most are not very fine-toothed, but at least you can try out the pull-stroke cutting action for yourself at a modest outlay.
If the thing you're after is a very thin-kerf fine-cutting saw, for dovetailing for example, it's very easy these days to get the impression online that Japanese saws are the only way to go. But of course this is nonsense because there has always been a need for this kind of cut in Western joinery. There are conventional Western backsaws of the "gent's saw" style, that have blades every bit as thin as their Japanese equivalents. These may be marketed as razor saws and in some cases they have extremely fine teeth: 32tip and above are available.