Though I've had many oppurtunities to join Herocraft, I did not take one until this past January as the wonderful server which I had been playing drifted away into oblivion. I joined Herocraft because of the Heroes plugin. I only play one server at a time, and once I get into it, I don't leave unless something happens that completely drives me away or the server dies. In order for a server to interest me, it has to offer something original (in terms of MC). I played many servers that we would call generic today. These were all in the very early days of MC SMP, in which basically everything was original. I played a few more following that, but they bored me because they had nothing new and I didn't stay very long. I didn't think of Herocraft at the time, and ended up joining a zombie survival server which I stuck with until January. Original? No, of course not. But original in terms of MC? Definitely, it was the first. When it died due to some very bad luck, I came here. Herocraft is a hardcore MMORPG with awesome skills and classes. Original? Not at all. But original in terms of MC? Yes, and though there are some a bit like it, none are as good. Heroes drew me to this server. It is why this server is original and unique in these days where all MC servers seem bland and monochromatic. If Herocraft were fairly vanilla with towns and spells hidden in dungeons today, it would not interest me. A year ago when that was fairly new, if I had seen it, I would've probably joined. But today, too many other servers offer similar things.
Herocraft seems to me to be a pioneer server. When it came out, it was pretty normal save for some newer plugins. As other servers got plugins like those, Herocraft advanced far ahead. There was never any competition for the community that gathered to HC because no other server could offer what HC had. If Herocraft stopped doing new and interesting things, it would still be big for a while, but then other servers would catch up. If someone, oh, say, lost all their gold on an HC like that, they might just start over elsewhere, whereas most people in a situation like that in this HC would stay because there is nowhere else like it. Even smaller things than losing gold would drive people away because there would be nothing really keeping them here. Communities would spread out through the servers like that hypothetical Herocraft, grow bored, be attracted to another server that advanced forward, and the community of the hypothetical HC and the other stagnant servers would be spread so thin that (with the exception of fully self-sufficient servers) not enough donations went to each server and they'd all die out.
Herocraft changes rapidly and drastically, it seems. If it didn't do that, it would stagnate, and the community would diffuse throughout other servers that caught up with the hypothetical Herocraft. This server has been around like... two years. This is only possible because Herocraft always manages to have something new and appealing that no one else has. Herocraft would be dead if it did not advance from what it was in Sanctum. Sanctum was new and original then, but it would not be now. True, most servers who stagnated at a period where they were similar to what Sanctum was are dead, so bringing back a Sanctum server would be original for a while. But if people saw that that was popular, they'd make clones (easily, too, because similar plugins to what existed then are readily available now, and many good builders are ready to work), and the community would spread thin. Herocraft would have to advance again to survive.
I don't know if Sanctum or now is more fun. I am fairly certain, though, that if HC went back to and stayed at a Sanctum-era level, it would not last very long. Are all the advances that have happened good? No, surely not. I think MA is a very detrimental thing, really. But many of them are good, and they've kept the server alive.
Another issue: A very large portion of the HC community joined post-Sanctum, and even post-Zeal. They joined because of something HC offered at that time. There is a certain number of people who stopped playing but still watch HC looking for changes they like, but not nearly all the people who don't come ingame anymore still monitor HC. Reverting to Sanctum would drive off many of the users who joined after it (a large portion of server funding). You'd have to assume that the amount of people who would become active again would be enough to make up for that funding loss, and that assumption is probably wrong. A lot of people, when they quit a server, really quit it.
I joined in mid-January. I did not play Sanctum. I don't know if it was more fun or not. All of the above is based on my knowledge of HC today, of what other servers/plugins exist, and my limited knowledge of what HC was in Sanctum. I am very possibly wrong, but please at least consider what I've said.