Inventing new mutations

There never seem to be enough of them... mutations I mean. Although Gaia Gamma will contain many dozens (most likely far more than 100) mutations you probably will soon want to invent new mutations. Today I would like to present the simple rules I devised for that. They are inspired by Nexus: The Infinite City, a roleplaying game I heartily recommend for anyone interested in strange parallel universes and genre mixes (and the precursor to Feng Shui - another great RPG).
Here we go with the rules for inventing new mutations in Gaia Gamma:

It’s up to the Mutant Master to invent new mutations. The following guidelines should be respected:

• New mutations should not cause any existing mutation to become completely useless (for the same MP cost).
• New mutation should be aligned to the damage potential of existing mutations.
• New mutations should not enable time travel or other reality altering effects (such power was even beyond that of the Ancients - at least as far as character creation time goes... you never can know during the actual campaign).

The most difficult question probably is about determining the cost in MP for a mutation power. Use the following guidelines to calculate the total MP cost:

• +1 MP if the mutation is very versatile (e.g. telekinesis)
• +1 MP if the mutation causes damage or protects from damage (e.g. claws or armor plates)
• +1 MP if the mutation has a ranged effect (e.g. laser beams from the eyes)
• +1 MP if the mutation has an area of effect (e.g. fire breath)
• +1 MP if the mutation is highly useful (e.g. telepathy)
• +1 MP if the mutation works automatically without the need for activation
• +1 MP if the mutation is associated with a mutation skill and thus can be improved

Again that's it. Simple and straightforward as far as I am concerned. What do you think?