I've been playing T9A for a number of years now so perhaps I can bring a different perspective here.
The first thing to understand is that T9A was started as an actual sequel to 8th edition fantasy, but most people who play the game and (perhaps more importantly) develop it now see it as a different game that was inspired by 8th edition fantasy rather than a sequel. Most players did play 8th edition, but there is a growing playerbase of people who never even played GW products. VC are currently very similar to the GW version, but haven't had a full redo yet, and the tendency in the full redos is to move somewhat away from the GW conception of the army (this isn't universally true though). Most long-time players of T9A now get more confused when people use the old GW names rather than the other way around, which is kinda funny. The general impression that I get is that most players who have switched to T9A have very little desire to stop playing when TOW comes out.
The number of players does depend strongly on your location. As far as I can tell, the game has a very strong player-base throughout most of Europe with every second Polish male trained from birth to play ninth age (a joke; but many of the best players are Polish). In North America, there are large swathes of the continent with only a couple players, but also smaller cities that could easily hold close to 50-person events so you really have to treat it on a case-by-case basis. If you go to the ninth age forums and post on the national forums, you should be able to get more region specific information. If you are willing to play online, there is a quite active online playerbase.
As to the rules themselves, many players have expressed the frustration that the main rulebook is hopelessly complicated to read through. The rules are, in fact, of a similar complexity to 8th edition, but the designers of T9A (for better or for worse) have sought to clarify every possible ambiguity that could ever arise over the course of gameplay. This is fantastic if an odd situation comes up in your game and you need to look it up in the rules as the situation will be fully covered with complete unambiguity. However, it makes reading through the rules a lot like reading through a law dissertation. If you can find someone to teach you, it is probably preferable and the rules are ultimately fairly similar to 8th.
The rules are extremely well-balanced to the point that balance differences between the armies are almost irrelevant in determining game outcomes. The vast majority of units see competitive play. Because balance is so good, its actually a lot easier to make a decent list as there are no real 'trap' options to fall into. For better or for worse, most extreme RPS type interactions are gone, and "Purple Sun" type spells or units that can end a game in a single play are gone (no heroic killing blow lol). If two players of similar skill play, the vast majority of games are going to be close. If you like massive Purple Sun type spells and interactions (a "Johnny" type player to use MTG lingo), then T9A is probably going to be pretty disappointing.
Due to the balance and the clarity of the rules T9A is ideal for fair pick-up games between two strangers.
The criticism brought up about the frequency of the updates is now a bit outdated; there was a point a couple years ago when the developers were really afraid of IP issues with GW and so made a series of rapid updates to move the IP far away from GW, but now updates are pretty slow. Once per year there is a points update where all units are slightly adjusted in points based on all the data collected from the previous year. In addition, every few months or so an armybook gets a full makeover. In so far as I can tell, there are no other updates slated for the next few years. There is also the occasional supplement released, but most players do not use these or would ask their opponent before using them (tournaments almost never use the supplements).
Finally, due to the model agnosticism, you can convert and use whatever miniatures you want in T9A which is pretty cool. I have miniatures from a variety of manufacturers now.
Honestly, if you can try out T9A I highly recommend it. It is honestly the most fun I have ever had miniature wargaming. In 40k, I get so tired of looking across at my opponents army and thinking "well, this won't even be a game" and this simply doesn't happen in T9A.
I haven't played WAP, but have looked at it. There is way too many units to have quick pick-up games without a "explain what my army does" phase. I have never met anyone who actually plays it, but it actually looks like a lot of fun if you were playing someone you knew well and had a lot of time.
it's been so long I need to refresh my memory on them! 
