There IS a practical limit!
Kidding aside, there IS a practical limit to how many tools one has.... several of the posts already have alluded to space limitations and the need to stow tools away from the work area....case in point:
Several years ago, one of our woodworker club members built a very nice addition to his garage - well-supplied with electrical power, lighting, storage loft, heating, air conditioning, stereo, etc. - this started out as a really nice space. He is a "hunter and gatherer" from all manner of auctions and sales, and in the few years following the building of this new shop, he promptly filled the space with all kinds of power and hand tools, and large numbers of cabinets filled with various parts and supplies - essentially this shop has become a warehouse. There are boxes of things everywhere on top of stationary power tools, benches, and shelves that some day "will be put away" (.....but where?). There is not enough space to rip a 2x4, or even cross-cut it for that matter. Very narrow paths of rare "open space" now run through this "shop"; I don't think he's built a project in there in years. I consider this space totally useless, despite the fact that this guy has hundreds of tools!
Therefore, a somewhat serious answer to the original question is that when the number and volume of tools you own/have in your shop or studio begins to impede the process of actually working there and being productive and efficient with your time, THEN you have too many tools.
Since humans, and especilly woodturners, are creative people, there will be all manner of creative solutions to store one's tools safely (....although I've seen some TERRIBLE, unsafe storage solutions), and still have ready access to them when they are needed. The majority of our tools are narrow and slim, making storage and access pretty simple by comparison to flat-work tools. Thus, the number of turning tools can be quite (even ridiculously) high. Once this tool volume begins to get in the way of safe and efficient work, the "too many" boundary has been reached!!! Maybe that's the best definition?
Cheers,
Rob Wallace