I have 7 expansion packs, The Trombone was the most useful to me.. They are all decent. Yamaha is very calculated about their packs. While they are improvements, one does not absolutely have to get them.. Yesterday I realized I have bought 137 products for the Tyros over the years.. The styles can be downloaded again no problem.. The midi's are limited in how many 'downloads you have available'.. only one left of those).. I have the purchased Midis on my computer, so that is a complete non-issue.
I downloaded a lot of styles form PSR.. After a while.. I notice that, one can combine different instrument parts of various styles, to complete or somewhat duplicate the desirable aspects of their new styles.. Still I was a bit shocked to realize how much extra $$$ I have invested in additional Tyros styles, premium packs, etc. I certainly don't regret it..
I think Yamaha is one of the most 'user dedicated companies' in existence.. I have several IK multimedia software products. (virtual instruments of DAWS). But their general attitude is once they got your $$$ they really don't give a crap.. They make good products, but treat their customers like crap.
We should be grateful for Yamaha's unsaid motto - (the customer is important)