I've not done either of these tours but I have done a number of back to back or in one instance back to back to back tours! I love doing them.
The ONLY downside to me is that I learned that I enjoy them more if they are different cultures which yours definitely are. I did Southern England and Scotland and was pretty bored with castle ruins by the time we were part-way thru Scotland. A few years before that I did Best of England and Paris and Heart of France and really enjoyed that. Very different areas, different food, different scenery.
IF the dates work out, I'd do at least 4 or 5 days in between tours. First, to travel without stress to the new destination, then time to rest up a bit and get some laundry done, time to "forget" the names of tour members on the 1st tour and allow yourself brain time to be ready to learn a new set of people. In your instance, brain time to switch from Italian to Polish!
I'd go for it! Carpe the h*!! out of that diem!