I often translate files for the same customer that require the same glossaries, TM, etc. I always do this in the same project, **even though they are strictly speaking different projects**. Is there any reason why this would be a bad idea? I can't think of one, but I hope I'm not overlooking something.
When you say "even though they are strictly speaking different projects", I assume that you mean that they are not part of the same assignment (purchase order) from your client. However, if one broadens the meaning of "project" to include all assignments (purchase orders) related to a given client, TM, etc. with common terminology, then your approach would seem to be most appropriate.
The only possible disadvantage that springs to mind is that the 'project' would not have an end date but would continue for as long as you continue to get orders from your client, which relate to a common TM and terminology set. This is, as far as I can see, more of a theoretical problem than a real one.