+1. In fact, after a time, it can be easier to get your limit raised than lowered (at least that has been my experience in the past).

As to your particular strategy, you may not even need credit cards. The best way to get seat upgrades is to get elite status, and the best way to get elite status is by flying. Since you're already flying a lot, if you haven't done so already, you should sign up for your airline's frequent flyer program. You should also, if you can, consolidate your flying onto one airline, so you're accruing, say, 50,000 miles on one airline, as opposed to 10,000 miles on five different airlines. You say you're a "world" traveler, so I assume you're flying a lot internationally. Always make sure to fly on the international airlines that are partners with the domestic carrier that's your "home base".

Some credit cards will give you "EQMs" -- elite qualifying miles. This depends on what airline you fly. But it is possible to get a few (maybe 10,000) EQMs with a credit card. I call that "a few" because elite tiers are usually every 25k, so 10k doesn't do all that much for you, though it can be a nice bump if you're close to the next level.

You can, of course, apply for lots of credit cards to get miles. You can redeem these miles for trips in business/first class. You can also use miles to upgrade. The particulars vary by program, and for this we'd need to know what airlines you tend to fly. But if you are flying a lot for business, you probably don't have lots of flexibility re your schedule, etc. So the easiest way to get upgrades is by elite status.