Last year all the Cedar Fair parks had Fast Lane, which let you skip the line for popular rides for a price. Basically the parks that now have Fast Lane Plus will charge a fee on top of the Fast Lane fee to be able to skip the line on the biggest and most popular rides. Or in some cases, the ones with the longest and most tedious lines.
Take for example Kings Island, where the Plus option will let you skip the line on the Beast - still one of the most popular rides there - but also Firehawk, which is known for its slow loading process and thus a long line. Regular Fast Lane will not let you skip the line on these two rides, but if you pay an extra $10 for the plus option you can.
The prices for the feature vary by park, and Plus is not being offered at them all. It looks like only parks with a large amount of rides already a part of Fast Lane are adding the Plus option. On July 4th you can can two Fast Lane passes at Cedar Point for $70 each ($140 total) or if you want to skip the line for GateKeeper and Top Thrill Dragster you can upgrade to Plus for $15 more ($170 total).
The reason I mentioned Six Flags in the opening line is because they've been using tiered Flash Passes at some parks for years now. I just priced Six Flags Over Georgia for two guests on July 4th also, and the price for two ranges from $60 total for two passes at the most basic level, to $165 for two for the Platinum level which includes Dare Devil Dive and other bonuses.
So really, Cedar Fair's new Plus system is essentially making them more in-line with what the industry is already doing. Other Cedar Fair parks listing the plus option are Canada's Wonderland (Behemoth and Leviathan), Carowinds (Intimidator and Nighthawk), and Kings Dominion (Intimidator 305 and Volcano).