Any chance of a nade kill counting as a "level up" achievement for people not on nade level? For instance, killing a player with a nade you picked up from the top of the churches does not level you up if you're on knife of below.
Also, on some servers, you get a "speed bonus" for about 15 seconds if you get two or three knife kills in a single round; e.g. you walk/run faster for a period of time. This is a feature that was pretty fun on other servers and may be something worth considering. As for health bonuses for knife kills that other servers have (+20 health or whatever for a knife kill), I hate that shit and I'm totally against it.