Wow I have no trouble seeing my guages at night with my dimmer set almost all the way dim. Sure I can see it more profoundly when its on brighter, but I have it set to as dim as I can have it without it being unreadable. I can still read it all perfectly with it very dim.
If yours is dim its possible there is low power getting to the bulbs, and the low power could be because the dimmer module has a problem and it not sending out the right power.
The bulbs being worn can also be the problem.
Personally I like my Dash lights to be as dim as possible. Mine can get very very bright to the point where it almost glows and produces enough light to light up the interior.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.