No first turn Russian attack is more than saving the fighters
Finland has 3 infantry, 1 fighter and 1 tank, and they can all get killed on a first turn attack by Russia. The losses from that battle alone are worth (3*3 + 5 + 12) 26 IPCs. When I play as Germany, if Finland isn't attacked on Russia's first turn I usually attack Karelia using all available ground forces, just to retreat before round 2 to extract all but one infantry from Finland. Now of course this isn't always possible: if Russian really stacks Karelia well then even one turn of attacking can incur unacceptable losses, but you might be surprised how many people leave too many Russian infantry in the Caucasuses, which opens them up to my Finlandian retreat. So if we discount the 26 by the 1 inf being left behind we're at 23, then another fudge factor to account for the times when my little 1-round gambit is too risky and maybe the valuation is down to 12. That's pretty close to the spread between the bids on Russia attacks and no Russia attack games.
And we haven't even talked the risk that Russia can take Finland and kill the fighter in the Ukraine (although both European attacks might stretch Russia a little thin).
Finally, Asia. I don't count this one for much (in terms of Russian upside). Sure, Russia can take out the Manchurian fighter on the first turn if they really want, but to be safe that probably involves using the fighter from Russia, which isn't available if they attack Finland and/or the Ukraine. Plus, as Don Rae rightly points out, the Manchuria attack puts Russian troops in a dead zone where they can be directly attacked by the Japanese navy (see Turn 1 under the heading The Right Japanese Typical Purchases and Deployment Strategy). In fact, if Russia attacked Manchuria and left some tanks and armor there I would probably not attack Pearl Harbor just so I could use my battleships and extra aircraft in the battle to make sure I won. Wiping out the Russian tanks on the Eastern front pretty much opens up Russia to being dominated early.
So as an Axis player, I put a high premium on the no Russia attack rule. I think it saves me between 12 and 23 IPCs as Germany. Granted, this is equal to the cost of the 1-2 fighters you suggest saving as an alternative ruleset, but I value the units I've saved more. Germany needs tanks and infantry early as much as they need planes, and I'd probably only lose one in a first turn Russian attack anyway (almost noise compared to what I might lose on Germany's first turn taking out all the navies). That is why I pretty much only play no first turn Russian attacks.
Now to consider the Allied perspective. The game is already unbalanced (see the link about bid spreads), so if someone wants to play me straight up with no bid, then not attacking as Russia is the least I can do (remembering that I don't consider giving up the Asian attack to be a concession at all; I wouldn't do it even if it was allowed).
As the Axis I would not take this deal
I would need more incentive that just saving my fighters to be okay with letting Russia attack in the first round. As the Allies I'd take the deal because it's not much of a concession (I'm not attacking the fighter in Asia and the one fighter I give up killing in Europe doesn't unbalance the game enough for me to be worried at having a chance to win).