Last season he scored 24 goals in 30 appearances and was city's top goalscorer. He's only too expensive if he gets injured. This season there are many very good midfielders for the 6.5-8.5 range,you don't have to have Haz/Sanchez. You can field 4 of them and still afford an Ibra + Kun fwd.
Agreed. In years gone spending £24.5m on two fowards would have severely hampered the midfield but as you say there are a lot of good mid-range options this time around. It used to be like, Ronaldo, Lampard, Fabregas, Gerrard etc all desirable in midfield but also really expensive.
I also think people tend to overlook the 'force multiplier' of the armband meaning that having an ultra-expensive player isn't quite so damaging because you can get double-value out of that extra money when they are captain. It effectively means you can field an extra £13m player every week if you want. If you have an extremely balanced squad with everybody costing under £10m then you can't really take full advantage of the armband (unless of course an elite player is massively underpriced but that generally doesn't happen often and if it does the team with the luxury player can probably afford them as well).
In years gone by I've shied away from some luxury players (I think RvP was £14m one year?) but weighing it up this time around Aguero was one of the first names on my teamsheet - fit, playing for a top team with an attacking philosophy, relatively low rotation risk, best striker in the league, proven track record in FF, lack of too many viable alternatives etc (I was tempted by Costa but wasn't 100% sure if he was going to be first choice at Chelsea once the transfer window closes). He has a dodgy injury record however being the most expensive player in the game means you can always replace him with a decent option, it's not like when you get an injury to a cheap striker but have no budget to bring in decent replacements.
Finally he's also one of few players with pure explosive potential that can really kill you if you don't have him an a rival does - whereas missing out on a top performing defender can lose you points it is unlikely to cost you more than a dozen at the most in a given game week.