The basic rule that most people play with is that you cannot model for gaming advantage- if I feel I would get an advantage from a mod I've done then I take all disadvantages of the my mod, but dont take any advantages: so if I had a unit on some really thick scenic bases making them much higher up then usual and I was behind a wall I wouldnt normally be able to see over I would let the opponent shoot me, but I wouldnt shoot back (he can see me- I can take disadvantages of mods, but I cant see him since thats an advantage of the mod). I've never had anyone argue with anything I've changed or used based on these guidelines... and since all the MCs in my nid army used to all be the much smaller 2nd ed models (I dont really use MCs anymore, other then my trygon converted swarmlord) it was a problem I ran into a lot.
Of course there is always the fall back position: if it looks cool few gamers will care if its a benefit or not (unless its OTT)... if it looks shit and is obviously only done to get a bonus no-one will be happy with it...
Of course there is always the fall back position: if it looks cool few gamers will care if its a benefit or not (unless its OTT)... if it looks shit and is obviously only done to get a bonus no-one will be happy with it...