Holy crap man! I knew the M45 resembled the Mercury Marauder in a way, but that Continental concept looks very similar to the Y34 in shape and layout! So, either Lincoln was lazy and copied a Japanese car (that copied other American cars) or the M45 is somewhat futuristic, lol.
It was a very polarizing design as you'll learn. Not too many people have looked at my car and ignored it at first glance. They either like it or hate it, although I've seen it growing on a few people who absolutely abhorred its looks at first. Obviously, Ilya isn't one of these people.
One thing about the reliability is that as much as they seemed to consume oil when they came out, these are reliable engines when kept up with maintenance. I'd like to hope that the bad ones were all caught and replaced within the warranty period, or that the cars on the road didn't have issues.
I don't know what the magic sauce is, but there have been periods where my VK45DEs showed very minimal oil consumption, if at all.

As a tangent, did you do the maintenance on your GS by yourself? If so, did you always drain out the same amount you put in during oil changes or did you see some oil consumption?
I honstley like the way the M45 comes factory as long as it has the darker grill. I don't know if the color of the headlight bezels vary or some are just way to yellow over time to see but I like the darker bezel on those also (I feel like there's a light silver and dark gray).
A classy car, that is hard to screw up when it comes to wheels. I've seen some that are definitely not my type.
They have silver/grayish grilles from the factory but some people address paint peel by just painting them darker. They should all have dark headlight bezels unless, you're seeing lens glare or plastic fading.
In regards to the interior, the GS wins with the gauges, seats look more comfortable then the M, the Navi I think wins in the M because it's much newer though, a loaded M has way more features then a GS.
I have NAVI in my newer cars, but it's nothing to write home about. I think my phone's google maps trumps OEM Navi any day.
I've been in a GS300 and the seats were definitely nicer. Neither heated nor cooled, but they felt like a nice plush glove cradling for the tush - good for the highway. The M45 one is a tight baseball glove that will ensure you don't slide in corners, and you could get them ventilated.
Ugly is not a word I throw around much, but that is the badge that Lexus gets from me when it comes to the center stack of that period. The dashboard and controls area are repulsive enough to keep you looking nowhere but through the windshield or at that beautiful instrument cluster.
Performance
The M45 will outrun many vehicles from 2003, and even newer ones. Stoplight championships might not be its forte anymore, but passing on the highway is a breeze. Powerfully effortless cruiser that will get you to your destination 8 hours away with a smile although at the back of your mind you'll ask yourself if you could have used a butt pillow to your advantage.
I'm also looking at 03-05 FX45's which also suffer from oil consumption & cracked dash boards. The 06-08 fix all those issues but there out of my price range and the most i'd pay is $3,500-$3,800 with 140k max miles. 4x4 and SUV that handles like a G is intriguing also.
You seem like a V8 person, but I'd recommend an FX35 as well if you care for handling. I've never seen a cheap FX45 but I've seen some crappy ones for big money.
Where I'm from, you can't get a GS300 or GS400 for the price you can get a comparable M45. Typically you get more features, tech and performance Dollar for Dollar in an Infiniti. I reckon reliability is the same, but hey old perceptions stick around and I benefit.
Another thing, a cheap Mercedes is an expensive Mercedes. It will take you to the poorhouse with the neglected things you have to fix. A cheap M45, on the other hand, probably just has bad interior and dented exterior. It's pretty difficult to neglect an M45 to the point it becomes inoperable.
It can be maintained with Nissan components, unlike the Lexus we had that Toyota dealerships wouldn't touch.
Still on performance, segway into the aftermarket...
I have many brand new after market parts for the GS400 from tail lights, leather seat covers, front lip, which would make sense to buy another, but this M is intriguing. I just want to drive the M with no cosmetic modifications until summer and maybe wheels.
Some aftermarket components are shared with other platforms, but if you like cheap mods, the M45 ain't it.
The M45 wasn't traditionally regarded as mod friendly when it came to sound systems either, but these days people are doing things to them. Otherwise, the stock sound system is very... decent.
I'll tell you with no shame that Nakamichi beats BOSE all day, and twice on Sunday.
Oh, and if you ever have adult rear seat passengers, the M45 is surprisingly small inside.
If you've been test driving them, then this probably won't surprise you.
Let us know any exciting prospects you run into, either way this goes.