I tried that when I took over the rF2 club. Trying to get more different races, and not the continuous S397 Endurance and then S397 GT3. Had some BTCC cars with GT3's, those had 9-14 drivers. Tried a GT500 & GT3 race, that ended up being a GT3 race. Did a couple of Alpine races. First was very popular, then it fell down to 10 drivers +/-. Later on the guys who made the ByKolles made a couple of GT500 cars, so we tried a SuperGT event again with those GT500 cars and the GT3's (as that's basically GT300). It was very popular, at least the first race. Half the grid was gone for the second event, and when it was reverted to just GT3's afterwards, many came back.
There was a race with the LMP3-car only, dubbed the "Prototype Challenge", it wasn't that popular.
When the BMW M4 DTM was released for free by S397, that was supposed to be used. It took a lot of testing to find a fun track with DRS zones that worked with the car. But with only 5 sign-ups it was no other choice than to cancel it.
We tried to use the Mercedes 190E E2, the DTM machine from the 90's in a couple of Friday events, part of a pay-mod, but given for free. Didn't get 10 sign-ups even over 3 weeks. Tried with a modern, up-to-date S397 track, a track from the correct era and a good mod-track. No luck.
Going back to the GT3 & Endurance combo, in addition to big tagging sprees have helped lately.
Now, I know this is sounding negative, and I don't mean it like that. Some weeks I have time to test different stuff, other weeks I have no time at all. I won't stop, but when there's a sudden and massive drop in sign-ups that's demotivating. That often happens when there's an attempt to do something different.
I'm not opposed to try different stuff, in fact, I would love to do different styles of racing, different cars. Different types of multiclass. And it doesn't actually matter if the BTCC/Ginettas etc have a tiny fuel tank and only lasts 20 minutes. Then they have a 2 stop race. It's all a part of multiclass. I see absolutely no issues with that
I know the group behind the ByKolles and GT500 cars are working on an update to the GT500 cars, so I want to do another SuperGT event, but I would also love to have some, let's say, slower multi class racing. Like GT3 and GT4, or GT3 and Touring Cars etc.
However, few combos, if any have been able to both get good numbers and sustain them.
The only slightly different thing that seemed to be able to keep the numbers were the GT3 Sprints, where there was 2 races of 25 minutes, with one qualifying, and the fastest laps from R1 decided the starting grid for R2.
However, that takes quite a bit more organizing-wise, and it's not always I have that time.
We had a weird one with F3's on a Sunday last winter, 3 races at Lime Rock, only one qualifying, but the three races was on different layouts of the track. Was fun, but not oversubscribed
It was a risk with this GT4 car, but based on how it looked, who was working on it, beta-testing it and so on. I felt it was a pretty safe bet. It seems like I was wrong, which I am sorry for. Truly, and genuinely, I am.
I am however not sure that changing the second class
now is a smart thing. Then it's better to just make it a regular GT3 event I think.
Long post, but I've just finished almost 13 hours at work, so when I am a bit tired, I tend to ramble on. Sorry for that.
Lastly though, I'll repeat that I am more than willing to try other combos in regards to cars, classes, race types and so on. But that takes some testing, and when that often seems to not be that popular, it doesn't always feels that it's a good use of time.
EDIT: I have one special event planned. But I need time to figure out the best way to do it, how early to announce it, and if it should be a Friday or Sunday event.