I would put some shiny foil on the inside to reflect as much as possible. I would also connect it to a small transformer and see if a regulated power is better.

Yes I replaced my bulbs with led and placed them inside of the screw-in bulb holder and ran new wires down three times as bright. Search on eBay for model train replacement leds.
getting ready to restomod another will post the process on tinplate forum in the next couple of weeks

search for E10 based LED if you just want to screw in a replacement and not rewire

E10 AC/DC 4-26V E10 Upgrade LED Flashlight Bulb,

Thanks for all of the advice above.

Michael, it looks like your housings are bright shiny metal.  Mine are the gray plastic type.  Did your housings come on the tinplate car, or did you have to custom make them?

Also, once you mounted the bulb in the housing, did you replace the plastic lens over the bulb?   In my case, it may well be that the plastic lens is diffusing or blurring the light, rather than focusing or enhancing it.

Thanks very much,

Mannyrock

Get yourself a 10mm roundtop high intensity LED, you'll get a real spotlight effect!

Check out eBay: 161155955294, these are 160ma high intensity LED's.  You want bright, here it is!

Thanks Gunrunner!

I just ordered two of the pre-wired bulbs from them.

Mannyrock

My spot lights are tinplate brass with nickel plated brass inserts with glass lens. I sometimes forget there is a plastic world of trains. I only live in my metal train world LOL.

I think gunrunner sent you down the right track. Have fun see ya