With a clever pile-in you can get a lot of guys into range quite often. It is not too severe for Saurus because of their 32mm bases but I have managed to get 30+ Skeletons (those are on 25mm bases so the third row can fight if you use spears and get into base contact) into attacking range more than once, and boy, even though their attacks suck they become pretty devastating then, just because you are throwing 90 attacks at the enemy, and with Danse Macabre those might even be 180 attacks per round. Huge grin on my face, not so much for my opponent.
Ardboyz on the other hand don't have 2" range weapons available so my Ironjawz-playing friend often complains that big hordes are hardly worth it, because only one row actually can make attacks. The rest are just additional wounds standing around.
I think Saurus Warriors should receive a small buff to make them viable without having 40 of them. My initial, conservative suggestion would be to lower the threshold for the horde buffs, to 15 and 20 instead of 20 and 30. That would still encourage people to build big units (because of the point reduction) while keeping them effective below 30 models in the unit. It would not make them GREAT and it wouldn't mess with the complex synergies that are hard to put into numbers, but I think it would help. Then see how Seraphon players react in the next six months and react.
And yes that would still make 10 Saurus a pretty useless unit, but we have that for other armies as well, for 100 point units (5 Liberators aren't that great either although still better than Saurus).
Mm, so basicly unless you have the smallest base size, or are ranged like skinks, horde bonusses don't work all that well simply due to space constraints once you go past 20 or so units... Meh, I'd say that alone should be reason enough to look at how the mechanic works for most units...
A treshold of 15 and 20 would be better, but this'd still leave our summoning lacking with its max of 20 & I still feel it'd drop off too quickly (you'd still really only want to field units of 40 just to get the bufferwounds so they might actually survive a turn with the buff, 30 is only 10 wound buffer with a 5+ save, that's not amazing..) Personally I'd almost go for 5+ and 10+ given that they're supposed to get their bonus from organisation and not just from massed ranks. So even a handfull should get organised. Though especially the extra attack might need to be toned down in that case as that might be overpowered.
As for a unit of 10 being useless. I'd like them to at least serve some purpose. They don't need to be "good", but for example a unit of 5 liberators still fullfills its purpose. All it's bonusses still work. Its still sturdy. 4 groups of 5 liberators are not magically worse than 1 group of 20 in the same way that 4 groups of 10 warriors don't even hold a candle to 1 of 40. Hell, arguably 4 groups of 5 liberators might even be better as they can go to different place and can't be locked into place by being charged in a flank as easily, plus extra captains with bonus attacks. 5 liberators might not win much on their own, but they function, 10 saurus warriors don't even function on their own. Similarly 10 skeletons at least have the tarpit thing going with the ressurecting models. They might not be good, but they're not virtually useless against a different unit of 100 points.
Basicly, just make a unit of 10 actually decent line infantry like they're supposed to be. If I have 10 saurus warriors fighting 5 liberators I don't want the liberators to win 9 out of 10 times (without backup) cuz they just have vastly better raw stats nad their bonusses actually work in all (or at least most) situations..
To be honest, that's another big issue they have, all of their effects are conditional. In contrast the liberator's special abilities only have 1 that's really conditional (lay down the tyrants) the rest just kicks in in the appropriate phase. Re-rolling saves of 1 happens regardless. You don't need x liberators, there's no counter, it doesn't only work against attacks of type x. It just happens. It's odd that the saurus warriors have that many abilities and nearly all of em can be countered or only proc under a specific condition.