Parallax

I agree with Fulvio that the hi res rendering makes it look weird as it is, and I worry that if you bolt it on later on that the low res view will not look as good as it otherwise would if the game were developed in 320*2x0.

Beside the scaling thing, the position of actors, objects, parallax planes, and the cursor should IMO always fall on an integer low resolution pixel boundary, otherwise you'll get glitches that will break the "old school" illusion.

As of now, you could start rendering in a small, off screen buffer and stretch it in a nearest neighbor fashion.

Speaking of visual tweaks and retro modes: have you considered using a shader to make the final output resemble the look of a CRT screen from the 80s? I'm a fan of low resolution graphics in video games, but on modern screens they tend to look a bit harsh, losing quite a bit of their charm.

I did a quick search and found this site: http://filthypants.blogspot.co.at/2013/04/multipass-shaders-ntsc-motion-blur-and.html

Some of those shaders give the image a really warm, nostalgic quality. You could make such a shader optional, too.

Just a thought.

My two cents as a player:

I feel like this issue is actually of some philosophical importance to the project's original promise ("It will be like opening a dusty old desk drawer and finding an undiscovered Lucasfilm graphic adventure game you’ve never played before"), which made it sound like your ambition was for the game to be more than just fashionably "retro," but to actually have its own kind of anachronistic integrity.

At least to my eye, the visual force of pixel graphics is in the fact that everything onscreen exists within a unifying grid structure. The resolution constraints of the 80s didn't just happen to inspire the "pixelly" style that people remember fondly: the constraints WERE the style. Jaggedness and boxy-ness are just superficial consequences of the larger principle that gives it aesthetic meaning and power.

When modern "retro" games have objects made of big jagged "pixels" but still render in high-resolution and do away with the grid, they reveal themselves to be, at some level, fakes, merely exercises in nostalgia. Since the visual style doesn't have any deep coordinating integrity, it's intuitively clear that the designers didn't arrive at this "pixel" concept on their own terms — they just superficially copied it from another era. As a result, the games end up feeling like second-class creations. As a player, I can't get as invested in something if it's fundamentally an imitation of another thing, instead of confidently being a thing itself. Know what I'm saying?

So, whenever you do get around to it, I urge you to consider making the true 320 resolution mandatory — not to be "pixel-retro™," but actually the opposite: to be aesthetically cohesive, here and now, rather than just dependent on fuzzy sentimental memories.

I agree with you, but it also poses more problems (less so in a 320x200 resolution - and more in a 320x240) due to most people are running with widescreen monitors nowadays. Thoose aspect ratios cause oldschool games art becoming stretched in bad ways. Same goes for the scrolling and mousmovement in the scene which will look less smooth.