Several things to consider:
A - applying for a credit card is a temporary hit to your credit score
B - fully paying off credit cards regularly is a big plus to your credit score and making timely payments on outstanding credit cards is neutral to a plus
C - 'Responsibly' handing multiple credit cards over time is a big plus
D - Having multiple 'lines of credit' (i.e. credit cards) is a plus to your credit score
E - Having more bucks available to you as higher card limits overall is a plus to your credit score
I find that my credit score dips 10-20 points when I have just gotten a new credit card, opened a new bank account, etc. but within a month or two it goes on back up to where it was. I do not anticipate needing to borrow for a car, education, medical emergencies or a new mortgage any time in the near future (or even distant future) so I don't need to worry about a temporary dip possibly costing me higher interest rates. I try to use each of my cards at least every couple of months so that I can pay it off and add to my 'credit worthiness', so the real question I would have at the $75 fee is, "Could I get paid more for opening the card?" The bottom line is if you have the card and you got paid $75 to open it, if in 6 months you have an offer of $200 to open it you won't be eligible because you have it already.