I know he got an infection and blood clots in his legs from that fight but did it really have permanent damage and effect on his fighting style during the rest of his career?
Ali's a fool for taking that fight. He even thought Inoki was joking during the fight going on the floor, that was his legit strategy! His strategy was to stay on the floor so the boxer couldn't punch him, the boxer doesn't have strong kicking abilities (obviously). Ali was already shot after Frazier so I don't think it made much of a difference.
Muhammad's leg speed was on a downhill trajectory from 1975 onwards. More signifigantly and noticeably after Manilla. Ali's 'dancing' legs picked up a bit, after the FOTC,circa 1972-74 even though they never returned to their sixties best. The Inoki 'fight' was a dumb move for Ali and his camp to make.
Interesting observation. Of course he didn't really need his legs for that one. By then, he'd figured out that all he needed was to unload his lead right on his china chinned southpaw challenger, and time it to make good on his and Dundee's prediction of a fifth round knockout [written on the inside of his gloves before the match]. Mildenberger would have been wiped out pretty quickly by the veteran Ali of the Dunn fight. Ali used his legs liberally in Norton II and Frazier II, then became over reliant on his toughness to outlast his challengers after Foreman. [Actually, Bugner and Lyle used their legs against him more than he used his. Keep in mind that Ron was actually a little older than Muhammad.] Beyond his increased reliance on toughness though, his punch rate was respectable with Wepner during the championship rounds, in Bugner II [where he did most of the work], Manila, and with Coopman [where he did virtually all of the punching, and his challenger absorbed a lot of punishment]. He used his legs to limit his need to punch during the 1960s, but actually was capable of punching with a volume during the 1970s not available to him during his athletic peak [when he was in shape, that is]. Inoki certainly did him no favors, but I believe Shavers did more to permanently screw him up than Manila and Inoki put together. For Leon Spinks II, he did dance through most of the 15 rounds, but it was a rather ponderous Greg Page type of dancing.