Hi Man1,
I think there are some significant differences between the Libba scenario, and the Rocky/Beams scenario.
The most important is ceiling. Libba had a best season of 110 before his injury, and the other two had 132/122, that's quite a difference.
Libba was returning to a totally different game plan, and a Midfield of improved strength and quality. Rocky/Beams are returning to a Midfield that without them is probably the weakest Midfield in the AFL, and are probably more versatile to cope with whatever game plan Fagan comes up with.
I think the only way you can decide is pick a side with them, and without them, and weigh the benefits of the team with more dollars used in other areas, against the team without Rocky/Beams. I'd be surprised if there was a huge difference in expected points.
If you start without them, and they fire, you have to consider if you'll restructure to get them in, before their prices make it impossible.
If you start with them, and they collapse, there is no easy fix, as you'll be a Prem down on the better teams, as their prices make it too hard to go two Prems out, two Prems in.
What a pickle!
Beams is more pure Mid, but also more of an injury risk. Rocky can get shunted to the Forward line, and just can't string together high game numbers.
At the moment my approach is simple. Barring an outstanding pre-season showing, I'm not even considering either. The Midfield isn't for speculation, it's where, if your whole team isn't G'n'R, then really your Midfield should be. As you can guess, I didn't start Libba last season. Play it safe. Pick a team without them, as it will be easier to fit them in later, if the pre-season tells you to. It's much harder to take them out later, especially Beams, as the price makes it hard to find a replacement.
As to Fyfe, I think that is an easy one. Moving/playing ok pre-season, he just goes in your team. If not, he doesn't.