I also recommend
www.mymoneyblog.com for credit card bonuses and tips.
I've always utilized credit cards for rewards (never paid a fee or any interest, in 20 years). BUT, the past 2-3 years have been incredible on the bonus front. Being able to double up with my spouse, we made about $8,000 in two years. (So, about $2k/each per year). Other years more like $1,000 total (ongoing rewards).
Having a good credit score already, not spending money we wouldn't otherwise, and paying off the balance every month, has not been an issue. My MO is generally to open the credit card, earn the reward, redeem the reward, and immediately close the credit card. Even if there is an up-front fee, my experience is 100% fee refund when I close the card in the first few months. Credit score takes temporary hit, but nothing substantial. Of note, I also did a big 0% balance transfer game a few years back (when CD interest rates were more like 6%!). The last two times I refinanced our mortgage was ironically when was in the middle of these credit cards galore. It didn't affect the bottom line. So my FICO was 770 instead of the usual 820. It makes no difference - still the best interest rates. Last I checked I hadn't done any credit card deals in a few months and my FICO was back in the 800+ range. Same for spouse - we maybe both opened and closed 8 credit cards in the past 2 years.
If you don't have a solid credit score, aren't disciplined, would be encouraged to spend more than otherwise, then definitely don't do it. You've got to be a little non-average to make it work. Sure, 90% of the people who sign up for these things end up losing. I am sure FICO could be harder hit with different circumstances. Having a mortgage and a lifetime 100% on-time payments, I find it hard to hurt my credit score. I am sure my length of open history (I never keep old credit cards), and number of inquiries have been absolutely atrocious. But these are very small pieces of the FICO pie, in my experience. Keeping a good FICO score is important to me for insurance, working in the finance industry, being able to refi at will, etc. So I do keep a close eye on it.