As for DQ4, for the first time in the series, I feel like the western title screen is a major downgrade compared to the original. It's the beginning of a new trilogy, and I would *not* want to release a title screen for DQ4 in the western style.
Oh goodness yes, the DW4 title screen is awful. I don't think you'll find anyone who disagrees with you there. They must've been on some really tight constants or something.
While I think seeking out some expert help might be the only way (you could always try the help wanted forum). It COULD be just as easy, in theory, as comparing the NA and JP versions, finding where the logo graphics are relative to the castle and cloud graphics and maybe where the DQIV logo is in the JP version simply has all the tiles replaced with the DWIV logo. THEN do a trace log and find the ASM routine for the DQIV logo and replace the ASM for DWIV. That's still out if both our leagues, I fear hence why I said in theory. But then this game being so big, the graphics could be organized completely differently and could be programmed just as differently from the Japanese version as the DW1-3.
Basically what I'm saying is, it's probably the least changed title screen of the NES DQs so you have that going for you.
Edit: I was just comparing intros and they were WAYYYYY more different than I was remembering. I must've been thinking of DQV's intro with it slowly dropping in from the top. The JP intro just showed you a big sparkling IV on a black background and then cutting to the red sky with the full Dragon Quest IV logo while the US into has that ugly slab with the letters in Dragon Warrior revealing themselves before cutting to showing the TM and IV
Whoops, yeah that's much trickier than I thought. My best guess would be, assuming they're not shared with other map graphics. Remove the "slab" and have the tiles of the JP DQ logo reveal themselves than have it hard cut to showing the IV. That's my best idea.