On the matter of SA and UFO Lunatic being too hard when compared to the other games, what exactly are your problems with the games?
I cleared IN first, PCB after that, then EoSD, PoFV, MoF, then I got started on SA. Sure, it was hard, but ever after clearing EoSD almost all of my 1CCs boiled down to the mere question "How do I manage my ressources?". Both SA and UFO are filled to the brim with spots (tough ones, mind you) which you can just bypass with Bombs at little to no expense (Power gain is greater than the loss or equal, for instance); the only difficulty is finding out how to move, how much Power (or Bombs) to use up and which parts you should definitely make it through safely. Trying to figure that out, I'd just practice the stages again and again and again. There are so many ways of doing that that even weaker players should be able to get up to a certain point safely.
The way I see it, SA's and UFO's particular systems (overabundance of Bombs or other ways to clear the screen of bullets) were implemented exactly because the games featured rather tough patterns, to give weaker players a shot at beating them. The only problem is how to use those systems properly. If you cannot handle the patterns, use strategy - that's how I got to this point despite being, admittedly, not a particularly strong player. I use strategy to my advantage, and that's also what's fun about the games for me. Seeing new stages, new problems, then developing strategies on my own, practicing the last 30 seconds of UFO Stage 3 for the 250th time if necessary, just to figure out that I cannot safely squeeze out another Bomb there - no problem, I just adjust my overall strategy accordingly.
Admittedly, UFO strategy is tough, mainly because it involves lots and lots of factors. For most stages, I had to time the destruction of the UFOs down to seconds based on the BGM or other factors and even then there is only so much you can do in a single run without messing up, despite practicing each stage hundreds of times. And after that, I still only cleared 0/0, but given the level of skill I have, it was by far the most satisfying feeling of accomplishment I had felt - strategy overcame the odds. Mind you, it was a bad run, it always depends strictly on how many mistakes I would make. Theoretically, however, you can get through all of the Stages up until (and including) Stage 4 without losing a single life, building up your Bomb stock, picking up red UFOs occasionally to get to the Extra Life cap.
That's why I don't really see why SA and UFO are so different from the other games - they just require more strategy, more precision when bombing if you're weaker. That's exactly what weaker players have - not brawns (well, reflexes), but brains! Well, hopefully. Can't say I'm particularly big in the brains department either. Nonetheless, taking UFO Lunatic for instance, on my best run I got to to LFS with 2 full Extra Lives. On my worst with 0/0. That's the power of strategy! Of course, the 0/0 run was my actual clear, but that's the lack of skill I guess. LFS at the end was rather cruel because it put an end to everything I used to get to that point - bombs are useless (hell, they don't even clear the bullets properly!), Byakuren is nigh invincible most of the time and the pattern is hard. You can figure that pattern out or you can just call it quits. If I had to name one complaint about UFO, it would be that, though I don't regret anything. It just added to the satisfaction afterwards.