There I definitely agree with you. When they get summoned, they send the full-on aspect, no pulling punches. But when they're manifesting on their own, they're much more likely to manifest in a lower-Might aspect.
Let's look at Zeus for an example. Let's say, for the sake of argument, that he's Might 50. Clearly this fellow has a weakness for human women, and came to Earth fairly frequently on his own. But he probably manifest Might 10 or maybe Might 20 aspects for those visits. However, when it was time to have a worship ceremony where he was being summoned by vis, he'd come in full regalia with thunderbolts and the 50 Might.
Also, remember, that an aspect can't appear within several miles of another Aspect of the same Daimon, and no Aspect can return to the same location within a day of leaving it. So you can't spawn groups of aspects.
Perhaps some do. Or perhaps they're worried about Divine reaction. Or perhaps it's considered demeaning in the culture of the Magic Realm to do so. I'm not sure. But I'd argue that they do likely encourage their summoning in subtle ways.
This is my point. They appear from time to time. Not everywhere all the time. If they want to be summoned they would at least make sure their worshippers have access to all the vis they need for summonings. They might be a little cryptic about it "Go to the top of the Great Hill, find 24 golden apples and sacrifice them to meeee!!!!!!" Whatever the reason Daimons act like the time of an Aspect is valuable. Am I making sense?
I would guess that the frequency of appearance varies depending on circumstances. If you're the Oracle in Delphi back in 500 BC, maybe you see the aspect of Apollo all the time. If you're in 10th century Scandinavia, not so much. I'm sure the Daimons have their own agendas and they appear where it seems right to them. Consider, you might happen to run into Aneirin the Bard on the roads of Wales, just wandering. I'll bet he sends an aspect out like that to learn new stories. Yes, he'd like more worshipers or at least summoners. But he also likes a good story.