I think it is ok. The higher the price you pay, the more certain you need to be that they'll at least go close to last years output. Seems a bit obvious saying that, but it's amazing how many Coaches just lock in high priced players, without comparing expectation to price. The obvious example this year is Goldy, though for what we are talking about, it probably isn't fair to compare Rucks with Mids. If people are locking in Goldy, with an expectation he will be under 118 this coming season, or less than say 5/game clear of the 2nd best Ruck, I would say they are crazy.
Let's assume Fyfe is 100% fit. Unless you thought he'd be at least a 90% chance to be 116-117+ in 2016, then I wouldn't start with him. Going in with the a "I know he'll be top 8 for Mids" attitude doesn't cut it for me. Having said that, he doesn't become a Lock if you believe he will be 120, but he shouldn't be considered as a starting option, if you think he will only be 115. He is $670k. If he goes 115/game, then history says you will probably pick him up at around $550-$560k at some stage of the season.
I like your approach of banking the players with good on field history, that definitely lowers the risk. If you have set reasonable expectations, and those expectations are that the players at worst should score within 5/game of last season, then load up as many of those expensive 20+ game players as you can. The only thing I'd say to those reading this, is that one season of say 117, and a history of 103 - 108, doesn't make 112 a reasonable expectation for 2016. You'd want a bit more than 1 seasons history, to be paying top dollar at the start of the season.
