I'd absolutely agree with your statement that point victories are more common with experienced groups, but thats mostly because its easier to prevent dial victories.
 
This doesn't mean winning by the dial doesn't matter though - rather, its the case that the threat of dial victory forces all sorts of deliberate behaviours by players in the game to prevent this happening. As Nurgle has a hard time exercising this threat, his relative board control is reduced.
 
Tzeentch, Slaanesh and Khorne all (with the expansion in) tend to present threat along two angles for at least the first two to three turns of the game, and forcing your opposition to work to limit your dial advancement limits their options.
 
I'd also note that the length of Nurgle's dial is problematic because it takes one extra dial turn before he gets his first Upgrade Card. This, even more than the length to victory, is what makes him "dial-weakest" by far.
 
We've moved on a bit since our last post, and hit the magic 50 games. I'm no longer the dominant player, and now our win rates are pretty even as players (save for one guy, who always seems to be one step behind us strategically in this game). Even with a house rule in (first time Nurgle advances his dial, he does so once more for free) we've never seen a Nurgle dial win (though we came very close once) and we've seen slightly lower Nurgle win rates than the other gods. Tzeentch and Khorne are coming out very clearly on top, but this is happily proving self balancing to some degree, as the free-for-all nature of the game means that players will work very hard to deny Khorne even one dial advance counter on the first turn of the game, will always trickery from Tzeentch, and will often manipulate events so that a "safe Nurgle double advance" is preferable to a % chance of a double advance for any other player. The Horned Rat is proving hard to win with as well, as its often clear straight after set up whether he needs to play for points or dial (and predictability is a killer). Slaanesh is hovering in the middle ground, where he has many mediocre cards, subpar daemons, mediocre cultist numbers, a great Old World token to key off (but only two of them in setup) but is balanced by his shorter dial track and by Festival of Sinew, which is one of the best cards in the game for controlling the flow of the game.

I can happily state that I've played exactly 21 games of CiToW with the expansion in, as our group keeps the score tally. In those games, Nurgle has won consistently below average, though this is confounded by player bias: I've won just under half of the games played, and if we're free-picking, I rarely pick Nurgle. We've recently migrated to random gods every time though, so that has changed things a little.
 
My personal Nurgle record is three games played as him with the expansion, the most recent two of which using the house rule of a bonus dial advance on the first time he turns his dial. I've won with him only once, and that was a close run thing, even with the house rule in place. In contrast, when I've won with Khorne or Tzeentch I've often done so by a wide margin.
 
From experience I'd say Nurgle with expansion suffers a few key weaknesses:
 
1) He only has one feasible route to victory, whereas the other three gods can go dial or VP. Having said that, we are increasingly finding that Khorne is very much a points player with the expansion in.
2) His cards aren't as good as the other gods. There's some sweet plays he can make with regards to corruption counters turning up unexpectedly, but generally speaking he has nothing of the power level of Festival of Sinew, Glean or Hate. Generally speaking, a great card is one that has good economy, and which interacts with movement/summoning in some controlling fashion.
3) He doesn't have the drawing power of Tzeentch or Khorne, though he's on a par with Slaanesh.
4) He doesn't have quite as good upgrades as some Gods: Bloodletters and Horrors in particular are hard to equal.
 
On the other hand:
 
1) He has the most cost efficient lesser demons, and gains initiative advantage from that. This is far and away his biggest advantage, as being able to spend ONE point rather than two offers unparalleled flexibility, and offers the same board control (read: cultist killing power) for half the price Tzeentch, Slaanesh or the Horned Rat pay.
2) He can wrack up dial advance counters to equal the leader quite often, thanks to a combination of cheap board control, decent number of cultists, relatively easily met dial advance condition and cards that splash corruption about).
3) Its very hard to stop him placing corruption, one way or the other.
4) He doesn't rely on old world tokens for his dial advance condition.
5) He has a nice place in the player order - after Khorne, so he knows where the killing zones are, but before everyone else, so he can collude with Khorne to occupy both card slots, grab slots early, etc.
6) He has a nice low threat rating, so often controls Old World cards.
 
All in all, I'd say he's pretty closely balanced with the other gods, but just marginally weaker. With the house rule of extra advance on first dial turn, he's sufficiently competitive that the game works well, and the player playing him doesn't feel gimped. He's definitely the best at corruption and ruination, but not quite so much better at this that it compensates for his weakness at dial victories. He gets better the more experienced your playgroup gets, as a more experienced playgroup becomes more adept at making double-advance turns a rarity for any player, and this favours the VP game.