TL;DR, You have a 70% change of getting something helpful or irrelevent, and an 80% chance of avoiding anything (even potentially) bad.
Using your categories:
Harmless to Caster only 22%
These hurt other characters or only help the caster: 11
Harmless to Everyone 58%
These don't hurt anyone, or help everyone. Flavor effects are in here: 29
Harmful to Caster only 6%
These only hurt the caster: 3
- Potted plant (41-42)
- Polymorph (77-78)
- Frightened of nearest creature (67-68)
Harmful to Everyone 8%
These disadvantage or hurt everyone equally: 4
An outlier here is (69-70): Give everyone around you (but not you) invisibility. This means you might get attacked, but your allies will also get the advantage. It doesn't really fit into any of these categories (it is neutral in my system).
Using my categories
I chose to categorize the results in the much simpler: Good, Bad, Flavor, Neutral
Something that benefits you or hurts targets you choose: 23
Something that hurts you or puts you at an inconvenience: 5
- Fireball on yourself
- Confusion on yourself
- Turn into a potted plant (vulnerability to all damage): a minor inconvenience, unless you are on the front line for some reason
- Become frightened of the nearest creature until the end of your next turn: Basically just disadvantage on attack rolls for 1 turn.
- Polymorph yourself: If you fail the save you are stuck for 1 hour (or until someone hits you).
Something that doesn't affect anything mechanically: 12
Something that could be good or bad or neither: 9
This includes summoning non-hostile monsters, casting utility spells on yourself, and either helping or hindering a random target.
Note that in both categorization systems, 01-02 was excluded, because it just means more rolling for more effects.
You have a 10% chance to hurt yourself, but only a 6% chance to hurt yourself more than anyone around you and those 3 outcomes are all very minor, either only lasting 1 turn or easily reversed.
What can a Wild Magic Sorcerer could reliably be used for?
The same things any other Sorcerer would be used for. The Origin doesn't lose any of its spellcasting ability, which means you'll have lots of opportunity to blast things apart or shut them down. Sorcerers in general have less utility than Wizards, but there is still some there. Wild Magic Origins have a few extra sources of advantage and damage than others, with the cost that you occasionally (how often depends on the DM) get surges. Given that the vast majority of Wild Magic effects are either Helpful, or irrelevant, (70%) you don't need to worry about blowing yourself up, really.