I agree about all three of the games you discussed:
http://archives.tg-16.com/music_database.htm?col=en&val=legendaryhttp://archives.tg-16.com/music_database.htm?col=en&val=splatNOTE: I included a medley of ARCADE Splatterhouse (1988) for the sake of comparison. I really like arcade, but PCE's tunes hold their own! No shame.
I would add that Dungeon Explorer's chiptunes really enhance/complement the atmosphere of the game and the "action-RPG" spirit of a "quest" (whether you are safely exploring towns or battling the hordes, the music always feels right). It's not just catchy music, it is appropriate for the setting and the tasks at hand. IT IS EVEN MOTIVATING AT POINTS (when the hordes seem endless).
Of course, some of the underground caverns in Dungeon Explorer have the classic "underground cavern tune" accompanying it so I am in absolute heaven (I don't care how trite that formula is, I like it! I love the somber underground cavern songs in games from 8-bit/16-bit era).
You already mentioned some great examples, so, moving on...
UPDATE: folks, you can (1) download entire .rar or, if you'd rather not be bothered, just (2) listen to individual tracks in your browser...
http://archives.tg-16.com/music_database.htm?col=jp&val=dunSome favorite tracks:
17 Judas Dungeon (classic)
13 (give it a chance to build up! ~00:30 it kicks in!)
16 On its own, it might be annoying. It's a basic, simple track, but great in-game. I love the contrast between the lead synth holding, extending notes whilst the urgent, high-tempo background keeps grinding away relentlessly. Needless to say, that relentless rhythm matches the relentless onslaught of enemies, whilst the droning "organ" fits the mood of a dreary dungeon.
19 Final Boss (ATTENZIONE! HINTS OF LEGENDARY AXE II here!!!! Of course, this game predates Legendary Axe II...)
09 Melba Village (an upbeat song that starts out simply but becomes quite nice, indeed).
01 title—most folks haven't listened to the full track (I didn't until recently, since I'd press RUN immediately), the tune is really exquisite starting at 00:52 and overall sets a somber tone for Dungeon Explorer).