Depends on what you mean by top tier and when were they in the top tier?
My definition to be a top tier club would be ones who have won the CL or old European Cup, more than once.... not just domestic titles
So in the UK that's United, Liverpool and Chelsea, its a wider trawl in other countries of course, Real Madrid, Barcelona, Ajax, Juventus, both Inter and AC Milan, Bayern Munich.
Cannot think of any from UK, obviously RVP from Arsenal (but they haven't won a CL/EC) was valued, at least for one season, you might argue Own Hargreaves from Bayern, but he had injuries lurking and didn't go the full distance for us; all the rest of the big names who came didn't really pay off (except perhaps in shirt sales) and its possible Varane will go the way of Hargreaves in terms of injury issues
Seems 'top tier' teams don't do too much business with us, except to take from us (CR) in particular , but when they do sell us top players, they tend to be ones who are injury prone.
So my answer would be.... very little value!