There's little doubt that the better players tend to gravitate to the clubs which already have a strong squad, and given even money, I'd guess that most would join the club they perceive as having the best chance of getting silverware - maybe some players, hard bitten pros as they are, would genuinely forsake a little cash for a good chance of a medal. The old adage about 'being a long time retired', will always be true, but it must be nicer to have the odd memento to hang on to, or even pass down to your kids.
Sponsors providing non-cap input into things like training facilities, healthcare and more coaching staff is something we clearly don't have at anything like the levels of the top clubs, and obviously, we can't forget the influence of 'non-connected third parties', who may provide 'jobs' away from rugby or even work for spouses (and more if they don't stick to the legal, taxable elements, not that they ever would, of course
) - in the final analysis it all adds to the 'package' and may well be the clincher in a tight decision and is an area in which don't have any clout.