I'd question the need to get $150k out of a player starting at $300k. The real money is made with the base price players. Obviously, if your midpricer happens to increase by $150k then you can potentially straight swap him to a fallen premium but if you assume the standard upgrade takes two trades (one of which is cashing in a based priced player who has made the $150k), then the midpricer doesn't really need to have increased that much to complete the upgrade. Also, if he's punching out a 103 average to round 7 then you're probably keeping him (depending on the line).
It's been said many times but 36 trades changes the way we should look at this. There is plenty of scope for jumping off a midpricer who's made circa $75k-100k and jumping on another midpricer who's about the shoot the lights out. These opportunities emerge throughout the season just like they do in the pre-season. Ed Richards being one last season (although his emergence probably happened a little late to genuinely assist with team building)
Disagree with this, no real point picking them if they're not making as much cash as a rookie because it means they're not scoring as many points as the rookie.
If Hopper averaged 80 it would be the onfield equivalent of Baker averaging 42 and you'd basically never field a rookie that averaged 42 so realistically you're going to be dropping 20+ points on the rookie others are playing there instead.
For me the "150k" is more about the amount of points needed to match a middling rookie, the kind of guy you'd be starting them over. Guys like Hopper probably still make 150k if you're patient even if he averages 80 because there will be a couple of 110 games so if they're within basically 5 weeks of each other they'll do the job.
Basically you pay extra for 2 main things, job security and scoring consistency but neither of those matter if you're leaking 20 points a week, a consistent 80 against an inconsistent 62 in the above scenario still has you down 20 points a week on the rookie over a 6 week timeframe.
All of this assumes that you don't blow the cash and to be fair, this year the gap may diminish as I imagine many would be using the extra cash from Hopper down to a rookie to sure up their bench as it's definitely looking a bit like a premium rookie year but you still need that midpricer to cover the rookies.