If "good" players don't like factories and intermediate players do, are factories necessary to the game?
I'd classify myself an intermediate player and would say that the only country that really has any business building factories is Japan, and then not until the late game. The most common early game factory builds are usually mistakes, at least when playing against stronger players. A skilled Japan player will take out the Indian or Sinkiang factory in due time. And a skilled German player will have enough manpower to neuter a South African or (gasp) Egyptian factory if it is built too soon in the game.
That being said, allowing no factories for either sides is a common Axis & Allies variation, which I noted in my question, Recommended Axis & Allies alternative rules / variations?
I've played this variation a number of times and I've found it to shift the strategy of the game a bit. Without doubt, it affects Japan the most. Without the aid of factories, Japan must ferry man and material into Asia from the homeland. Since each transport can only carry a single tank, this forces Japan to go with a less than optimal infantry/tank mix. Moreover, it makes the battle of the Pacific more paramount, because if Japan loses her navy - or even suffers a heavy set back - her flow of troops to mainland Asia is impaired, if not neutered.
The no factory variation foists a dilemma upon the USA strategy - does the US still go full steam ahead with the "shuck-shuck" strategy, focusing on aiding her Allies in nixing Germany first, or does she use her IPCs to build up a navy in the Pacific with the intent of quelling the Japanese flotilla?
All that being said, to answer your question...
If "good" players don't like factories and intermediate players do, are factories necessary to the game?
They are certainly not necessary, but they make the game much harder for Japan without them. Japan's must have a prepared strategy and be prepared to execute on that strategy deftly. Little mistakes - like not correctly balancing transports with the number of troops in mainland Japan - can be fatal. Therefore, I think a no factories option is an interesting variation if the Japan player is a strong one, otherwise eliminating them presents an uphill battle for Japan that she might not be able to overcome.
And if "unnecessary," should they be permitted anyway? With or without modifications?
There are other units in the game that are unnecessary, no? How necessary are submarines, for instance?
Speaking of factory variations, the standard rules allow the factories that exist at the start of the game to churn out as many units as can be afforded, whereas factories built after the start can only output as many units as the territory's IPC value. Moreover, factories cannot be moved.
For your consideration, here are three factory variations. Personally, I'm not much of a fan of either, but both do color the game quite differently:
- Initial factories outside of the capital territory can only produce as many units as their IPC value. This has the most pointed effect on Russia, as her factory in Karelia can only output three units per turn.
- Factories, like AA guns and other units, may be moved during the non-combat phase. A moved factory could not output any units this turn or next, and would have its output restricted to the IPC value of its new territory once units can be produced. This option allows the UK to move its Indian factory out of harm's way (if needed), but on the flip-side it allows Japan to march factories closer to the Russian capital.
- When an attacker successfully invades a territory with a factory, he may decide to destroy the factory.
Food for thought...