Help with revising Summon Monster 1

[willpell]

Summon Monster I drives me nuts. The others in the series probably do too, but I haven't worked up the courage to look into them much. But just starting with 1, we see that you're given four Chaotic Evil fiends and only two Lawful Good celestials, with absolutely no options for anything that's Neutral with respect to Good and Evil. Some alignments get a flyer, some dont'; some alignments get an aquatic creature, some don't. That's all aside from the fact that the Celestial and Fiendish templates are crap, and that a lot of the animals aren't statted up very well either (why exactly can Monkeys not Jump?).

I'm not able to tell whether any of this is necessary for game balance, so I'm looking for advice on how it might be possible to change the options for this spell to be a little more balanced with respect to alignments and general capabilities.

[eggs]

For most characters, the Fiendish/Celestial aspects don't matter, so you may as well mix and match them. Except for Clerics, it won't make any difference (though this could permit some clearly situationally perfect options if allowed in play, which is both tactically dull and a slight power bump).

To restrict the number of options available for a given character (to avoid obvious optimization in selections), you could allow tradeouts or modifications to an individual character's summon list on a 1:1 basis during chargen.

As a guideline for the swaps, the CRs for the various SMs are:
{table=head]SM|CR
1| 1/4 to 1/2
2| 1
3| 2 to 3
4| 4
5| 5
6| 6
7| 7 to 8
8| 9 to 10
9| 11 to 12
[/table]
Creatures with powerful Sus or SLAs usually get clumped in with the next higher-CR group of templated animals, and creatures with niche applicability (like aquatic limitations) get clumped with next lower CR group of templated animals.

As long as there are direct tradeouts and enough DM oversight that monsters added and removed have approximately the same utility (most easily measured in SLAs), it should stay approximately balanced.