Firstly on NicNat. His price next week will be $561,900 +/-$300 and his B/E around 157.
If he can manage 110 the week after that, we're looking at around $541,200 and B/E 149.
A further 110 the week after that, and he levels out to $524,000 and B/E 102.
But as you mentioned, he's capable of landing a monster next week, and virtually "erasing" that 73 from his pricing pattern.
Secondly, looking at your team, I think your biggest area of concern is still your Def line. You are currently running Goodes D6 and Thurlow D7. That's very shakey, and little to no back up. Your other 3 lines need 2 or 3 to go down for you to get a donut, your Def line is hanging by the Thurlow JS single cotton thread. It's like the sword of Damacles, it's not if that thread will break, but when!
Let's look at it this way, if Thurlow disappears, you have no cover at all. It really seems like a case of when, not if, for Thurlow not getting a regular game. The problem with the approach of "But if I get Pendles and or NicNat, I still have a trade for coverage" is that coverage has no coverage. Sounds long and convoluted. Look at the scenario, that in the next week or two Thurlow stops getting a game (fair chance), and one of your 6 Defs gets an LTI. You use a trade to replace him, but you still have no cover! You have to hope your Def line coasts through 8 weeks with no Restings, suspensions or injuries! It's not a wildly inconceivable prospect.
Nine or Ten rounds is a long way to coast with 2 trades, and a line with little or no cover. It's a huge difference to what Chewy and Jay did, coasting the last 4 or 5 weeks with 1 or no trades, as they had good cover, or in Chewy's case, amazing cover in that last week!
Using SC Gold as a guide, let's compare your scenarios. I know SC gold is notoriously inaccurate, but at least it's a non-biased scale to measure things on.
Dal Santo > Pendlebury for the last 9 weeks - Dal 891, Pendlebury 1141, profit 250 points
Jacobs > NicNat for the last 9 weeks - Jacobs 692, NicNat 1100, profit 408 points
Long term injury to one of your 6 Defs - yours average 99.46 - 5 weeks of pain outscore NicNats gain!
I'm not sure what the easy answer is, though. Is it LOL Richo > Xavier Richards? This gives you a link to Staker and creates a FD loop between your Def and Fwd line. Richards is actually close to getting a run, if you guage his listing as an emergency a few times as a guide.
In the scenario where you get NicNat, AND Richards, you have 1 trade left for LTI's in the last 8 weeks. It's a long way to coast, but it looks safe than coasting 9 weeks with no Def cover.
Running the risk of no cover is a dangerous game, but taking risks is usually what making gains is all about. Your NicNat upgrade out trumps your Pendlebury upgrade (on SC Gold figures), and actually looks like a winner. Just keep an eye on your Def cover. You can very quickly cause more damage with no cover, than any upgrade will ever compensate.
Good luck