I also have never found any particular benefit to clearing the cache personally.
And I've often wondered if just leaving a lobby & rejoining is just as helpful as also clearing the cache.
However, I absolutely believe that for some people clearing the cache has been helpful sometimes in some situations.
So I've long wondered & suspected that it's most helpful for people who are running their console hard drive nearer to capacity.
We only have a few games on our ps3.
But some people have literally dozens of games shoved on their ps3.
Even more, some people are running GT6 on an older model of ps3.
So I've often wondered if that's where this cache clearing comes in handy.
But this is totally just a guess.
Heck, when there's a problem in an event room, I'd consider throwing salt over my shoulder & knocking on wood

and I'm not particularly superstitious.


But because nobody in the know steps up to explain why certain problems happen in online racing... we're left to just guess and try whatever. Clearing the cache is there... so that's tried with anything else.
I happen to be a big believer in rebooting the ps3 between different app activities.
And that's the oldest joke of computers is that's the first "solution" to any computer problem is to reboot.
But it's because sometimes it works!!
I worked for a small company doing IT years back, and the owner used to laugh & joke about this... because whenever he'd report a problem with his computer, or the server, before I could say anything, he would recite in this kind of mimicking mocking funny voice,
"Why don't you go ahead and reboot." and then answer himself,
"I know I know, I'll do that first." 
And of course, lots of times then there was no problem after reboot, and he'd laugh.
Whoever was there before me obviously had him trained... but he'd still want to mention that there was a problem before rebooting. Almost like he didn't want to be alone in seeing the problem. I understood that... it's kind of like when the car doesn't make the noise in front of the mechanic... The urge is there to have a witness!!
Anyway, long & short... so whenever I have a racing event... if the ps3 has been on & used for anything else, I reboot before going online racing.
I also clear my cache regularly... even though I don't even think that does anything for me.