Something I'm curious about is this: I see people with scores in the several hundred thousands per game. Are these games indicative of using these score-boosting methods, or because of a massive, planet filled galaxy? (or both)
Basically to hit the max score you need to do *everything* and of course that would include any and all "score boosting methods" known and imagined.
Clearly you want as many planets and mining resources as possible. You also want the fastest tech. Generally most people just use a shorthand and call these "abundant all" type games because that's literally what you want, everything you can get.
Ultimately what very well determines how high any particular game can score is the number and type of mining resources there are in the galaxy. In DL the average is 6 per type for a total of 30 but the most important are economic and military followed by research. Morale are nice too but usually having more of them is just a convenience whereas as far as I can tell influence are useless for scoring purposes.
As far as "score boosting methods" one of the most effective is to build up your pop, income and military as soon as possible. For the top scores this usually means that the galaxy has essentially been completely conquered before the end of the second year of the game. From there it's more a matter of keeping your approval high so that your pop grows fast and getting all the resources of the galaxy fully maxed out. Your income follows from your pop and your ability to build up huge quantities of ships follows from your income.
Let's say TA game, gigantic galaxy, all abundant. 8 year completion, no artificial score inflation, conquest victory. What would be the estimated score, ~350,000? How much extra score would the military rating-boosting methods give?
No real clue here. I would have to take "no artificial score inflation" to mean ending the game at the first instant that you possibly could without even allowing your pop and income to reach their final values let alone do any military buildup. In this case it really depends. If you can conquer the galaxy within a single year you could probably still achieve 400~500K. If it takes you 3~4 years to conquer the galaxy you might be talking about 200~300K. If it really takes you 8 game years just to conquer the galaxy then your score would probably be in the 100~200K range.
The same thing with the military buildup. If completed early enough it could add as much as 300~400K by itself, if completed 4~5 years into the game it may only add another 100~200K. The thing is you cannot over-estimate the importance of getting things done early in the game. I've seen cases where 5K ships built early can outscore 50K ships built late. It's not just a matter of what you do, it's when you do it that will have a bigger impact. That's why you can do exactly the same things I do and may only score 300K while I'll score 900K.
Basically people look on these "score boosting methods" as a panacea that will allow anyone to score any particular value they want ... they're not. Doing them will always improve your score over not doing them but usually not by as much as you would hope and most likely there will still be people that can not use them and score higher than some that do use them. However it is clear that to excel at the highest levels these are basically a requirement. You can't achieve the highest scoring games by leaving points on the floor.