Well, to be totally honest about it, I consider 40K to be a light/introductory level wargame too for all the reasons you listed. Crappy rules, crappy balance, lack of meaningful in-game choices, wind-up style play where the victor is often already known at deployment time, higher luck factor, etc... Light refers to the depth of the game, not the cost or number of models or anything else.
This game already looks much better than GW's stuff, and FFG does a solid job maintaining game balance so I have no concerns on that front. My main issues are all to do with things outside the game system itself. Factions, packaging, setting/theme, that sort of stuff. Areas where FFG does not have as much of a proven track record.
I'd love to see the game catch on, but as everyone here seems to agree, theme is a big factor for minis gamers. That means multiple things too.
1. You need a compelling universe and compelling factions
2. You need enough factions that you can pick one that you personally love and identify with. Note that in order to do this, the factions have to be highly varied, even divisive. In order to provoke strong positive emotions about one faction, there have to be ones you really dislike too. No number of bland roughly similar factions are enough. With colorful and highly distinguished factions, you still need at least four seems to be the rule.
3. You need stories and characters too. The Star Wars games have these, when you print "Han Solo" on a card, it comes pre-equipped with all kinds of emotions and attachments because we know who that is and we care what happens to him. On the other hand, if you make a figure of some fantasy dude with a sword and just write "Heroic Lord Swordguy" on it he's not a compelling hero just because you said so. He's just a generic hero, we accept that he's going to have special abilities and maybe be a stand by himself instead of a rank & file soldier, but that's all. Still don't give a crap about him, still don't know or care who he is or what he did to become a hero, and I do not feel any excitement to have him on my team the way I do when I put down Darth Vader in his TIE Advanced.
Given that a full game is 200 points and the demo was around 100 without upgrades, I feel that the cost of an entire army will be reasonable, provided that minis are sold in a reasonable manner and you don't have to buy other factions to get your upgrade cards. Going back to my point about factions, remember that your players should love their own faction and hate others, this is necessary to have the level of emotional attachment to your faction that you want. People simply cannot buy four or more factions worth of stuff to get their cards for one faction, and if I'm a Menoth or Cryx guy then I'm double dang sure not gonna buy any stupid pansy Cygnar stuff period no matter what cards come with them. That's like asking me to buy My Little Ponies to get the limited edition rifle I need for my GI Joes.