How about if the rockets were to start at 1 level higher?
I'm biased. I lean to playability. Playability, meaning, I want games that are 50/50 chance of winning, and players have the most options. Yes, giving the Germans an extra level of Rockets would tempt an Axis player to buy them. The Germans start with 1-chit of tech for Rockets. EVERYONE sells it.
I can provide you this information, seeing that I've played the most game (quantity wise) against humans. No one has ever bought Rockets. I did buy Rockets, in one game. It takes awhile to get their tech going. Obvious targets are London, Malta because of short range needed EARLY in the war.
As time progressed, the RAF/Royal was easily able to force German Rockets to leave the coastline. Only place to take, them is Russia, which is fine. Point them at Moscow/Lennigrad/Etc. Russians usually have pretty good supply except for Lennigrad. Thing is, against valid opponents, pressing Lennigrad doesn't win games. So yet not good bang for buck for Rockets in Russia.
About the only thing Rockets can do then, is to hide in France. WAIT, for Allies to land, and use to blast their ports and supply city. Thing is, won't have much of a chance against RAF/USAAF. The cost of the Rocket program will be expensive, so Germany won't have Mechanized Infantry pieces or some other better item, even Artillery.
Some of the historical speakers on the Forum, stated, Rockets were overrated in real WW2. Maybe they were. Just depends how you want the game.
So what to do? Asking me. I would give the Germans one Rocket unit, as an actual piece to enter the game, no charge. Could bump the tech up 1 also. Same could be said with Kamikazes :) I'd just give Japan some Kamikazes late in War.
Everyone has an opinion. The lower level player's don't win as Axis, that's actually quite historical. The Top players, and there's about 5 that are much higher skill level then the rest of us.