I'm an idiot, so I'll bite.
I am not even sure how, or IF you allow players to make spells. Here is how it works near me:
-Player wants a new spell and writes it up
-DM looks at it to make sure the level and power is right and adjust the level up if too powerful for the level, or down if he thinks it could work at a lower level than written.
-DM also can decide to just say no to it due to MANY various reasons of it being overpowered, too silly, whatever; within reason.
-Player makes needed changes, resubmits (sounds a lot like the publishing business)
-DM looks again most likely accepts if it wasn't rejected to begin with.
-DM looks at spell research to tell the player how long, how much it will cost, etc to research this spell
-Player decides if they want to spend that time/money doing so. The player likely already looked at the spel research rules when making the spell to present to the DM the first time.
TADA! new spell.
I don't think anybody disagrees with this process. You seem to imply that in YOUR game it can be done quite quickly. It's been my experience that this process should take several real-time days or weeks to design, review and approve a new spell created by a player.
Furthermore, at least with 2e, spell creation took considerable game time.
I suspect that a majority of D&D gamers agree with my assessment of how creating spells works.
As such, for MOST D&D gamers, creating a spell on the fly to solve the problem and save the day is not going to happen. Because there is not enough in-game time, nor enough real-time. As with the house-rules screws up games thread, a good GM doesn't approve new stuff like a spell without time to think about it. Which ain't happening in the middle of the game.
This is WHY most of us are pondering what you're getting at. Because for most tables, following the standard rules for spell casting and spell creation, it's not a viable solution to write a new spell to solve the problem.
What you are asking for is rules for magic. D&D has the approach that magic can do anything.
False. D&D, as published with the standard Vancian magic system requiring memorization for most classes, or a restricted spell list for other casting classes (wizard and sorceror respectively) has a very rigid magic system.
If you don't know the spell, you can't cast it. until 4e, you couldn't cast it if you didn't note that you memorized it that day (further limiting you).
And most spells have a very codified set of effects. Sure, effects like buffs can stack. But a fireball does level D6 damage to a certain area. That's it.
There are other games, and even replacement magic systems (Elements of Magic lets you create spell effects and combinations on the fly, as I understand it).
This leaves the game open for ALL playstyles. Yours where the players aren't allowed to just make things since you and them have no rigid rules for which to say what elements magic can have, and mine where magic can do anything, even autoerotic things that I do NOT wish to discuss...
Then it sounds like you're playing with an alternate magic ruleset than the stock one that ships with D&D. Arguing with people as if they were the same system when they are not is confusing and misleadiing.
You see your need for a rule as being a reason it cannot be done. I like how people throw out PAGE 42 for 4th edition, but ignore those such things in past editions.
All of which provides the tools for the job. You just want a precision tool without having to dig into your personal toolset for it, while others find the tools provided augmented very easily by digging in their personal tool set for the right tool for the right job.
Also you keep saying DM allows it, DM allows SPECIFIC spells, not the ability for players to CREATE spells. The game in nearly every incarnation has had the ability for both DM and players to create spells for verisimilitude.
You just don't want to use the tools provided as seeing them not adequate. I can appreciate that. I can't appreciate that the claim extends to ALL players and DMs.
Dude, you started this way off topic tangent. There's nothing wrong with your playstyle. But your tone since the beginning has had hints of antagonism. Based on your responses, each one seemed like YOU didn't listen or ignored points the other was making. What I smell is that you don't play the way most of us do. You are probably a minority on that playstyle of the D&D ruleset. The way you keep calling people out implies that we all need a lawyer to safetey check the way we phrase things just to avoid offending you. Thats disrespectful.
Nobody should have to preface every sentence with "In My game..." And most of us assume there is some variance in playstyles. However, it is also reasonable that each reader realize when they are in the MINORITY of viewpoint and most generalizations don't apply to them nor are they targeted at them.
Meaning, when folks like me said "Players aren't going to be creating spells on the fly to solve this problem" we were generalizing the experience for what we percieved as the majority of D&D tables. And statistically, we're probably right. If your table works differently, great. But don't go getting all bent out of shape because nobody else plays that way.
Not in any that I have played. 
