Hi, Cake...
I generally love alien scenarios, even when they're not tickling-centric. It's not like I have some separate erotic pull toward aliens or anything... but it seems that no matter who the author or the artist is, the erotic themes tend to be the same.
Here's my take from a writing viewpoint, but I bet you could apply it to art soon.
The human tendency to grow up believing in the absoluteness of non-absolute conventions such as manners, self-control, and authority serve to enhance the erotic quality of the experiences that threaten to break those beliefs. For example... in reality, there's nothing absolutely wrong (or even very remarkable) about being naked around the opposite sex. But, if you've grown up believing in the kind of modesty that most of Western society shares, and now find yourself in a situation where you're being forced to undress in front of the opposite sex, there will probably be a much greater emotional tumult for you than there would have been without that convention in your upbringing. In situations where this sort of trick is exploited by, or around, someone of the opposite sex (or the same sex if you're homosexual), then there's a great potential for these experiences to manifest themselves erotically.
Of course, for anyone to write about the exploitation of a poor guy or girl in this way requires the author to make up somebody devious enough to actually learn about the inner workings of the victim's mind, to be knowledgeable enough to plan whatever erotic experience the victim will endure, and to carry it out believably. That kind of a character takes a lot of planning on the author's part, and I think is challenging to write believably. On top of that, it might be conceived that such a character would have to be at least somewhat evil, and not all writers are comfortable with that either.
Aliens, however, are stereotypically known for traits that make all this easy. They can use telepathic powers, or advanced technology, to learn about whatever details of the human mind concern them. They're renowned for their desire to experiment on humans, and a psychological or physiological lab of any kind-- is believable. Finally, being such "different" beings than humans, they may or may not have experienced any physical or emotional feelings similar to theirs. Their concepts of "control," "humiliation," "tickling," "erotic," and so on, may be mere variables to them. So, not only could aliens be construed not to be evil in carrying this out, but even well-meaning.
The specific "what" they do isn't the source of the erotic power, but the idea that it's derived from a foundation like that. If you've got that, then I think you have a lot of liberty regarding the actual content. (At least, within the tickling cross-section. You can always link elsewhere if you have other themes.)
Finally, I must emphasize: when you say you "tend to create things that you fancy for yourself instead of the average viewer," I'm immediately much more interested in seeing whatever work you would draw for yourself, and much less in seeing what you would draw because you think that more people would like it. Definitely consider what other people have to say, but if you don't really relate to it, then your selfish work is guaranteed to be better.
