Bally machines will not work correctly with LEDs in the inserts due to flicker (GI is fine)
You can buy new alltek boards, or other boards to make them work or solder on resistors to each bulb socket.

If you're talking straight value I wouldn't think it makes a big difference either way.

Yes, if you are using color LEDs in the GI there are many people who think you are wasting your money.

https://pinside.com/pinball/forum/topic/no-rainbow-puke-club-post-pics-of-worst-color-gi-fails

Centaur is a great looking game with mostly a black and white theme. If you are going LED in the GI only use warm or sunlight white frosted in the GI to not hurt people's eyes or offend the color.

Opinion only but you asked. Simply, do not expect to recoup money you put into your custom changes.

I am sticking with stock bulbs on a Fireball Classic. There is a plastic on the left upper that is notorious for being unlit,
considering a 3 light warm white LED strip simply to avoid drilling holes in the play field.
I like colored incandescent bulbs over LED, thats what was used originally and plenty bright.
Also like the slow blink of incandescent over the fast flash of LED in the Back Glass.

In classic SS games I use LEDs for the controlled lamps and backbox GI. I use single LED clear warm white retro bulbs in translucent inserts since they look very close to incandescents. The problem with today's incandescents is they are cheap and can't handle the vibration. I got tired of lifting the playfield all the time to replace bad bulbs.

I generally like to keep incandescents in the GI though, especially if the artwork is warm colors. For space themes I can go either way, but I have yet to use cool white LEDs.

LED strips are great for dark areas. I used them along with sunlight LEDs in the GI in Xenon simply because the game is so dark. There are literally only 6 bulbs to light the lower two thirds of the playfield.

In Centaur, you'll probably want to keep incandescents in the GI because it flashes. The strobing of LEDs may drive you crazy.

I changed every bulb in my 1980 Alien Poker to led and personally I think it looks infinitely better. The game pops, the art pops, the colors pop, totally worth it. Pictures for whatever reason never really do it justice, it's best to see one fully led converted in person. For me a full led conversion is very desirable, and I know whenever I see a pin with old bulbs in it is means both extra cost for me because I know I'll fully convert it, plus I always expect those games with old bulbs to be in worse condition because of all the heat damage.

I light EM's with #47's mostly, and i work hard to color cordinate LED's with the plastic and the game style overall, so i dont get the clown posse effect.