[chevychic]

If you're bent on using the plug in replacement LED's and don't mind not being able to dim your cluster, just take some sandpaper to the head of the LED. This will cause the light to diffuse thus - wide angle. You could also grind down the top of the LED to take it from a curve to a flat with a dremel. This also spreads out the light. Just be careful not to hit the diode inside. When I did this on my cabby, I experimented with both and ended up grinding off the curve of the LED casing.

Robz- The biggest problem I see is that it's a range issue in the design of the switch (potentiometer). If you place a resistor before the switch, you still have the same range, just at a higher resistance which is cutting the power to the LEDs. It was this lack of range that I had a problem with. I just did not have a large enough range to provide a high enough amount of resistance to dim the LEDs adequately and provide a low enough resistance to achieve full brightness. For 2 5MM LEDs running off 12v with a 3.6v drop across the LED, the resistor value required is 270 ohms. If your maximum brightness setting on your switch is higher than 270 ohms after you wire in a resistor, you will not be using your LEDs at maximum brightness. When I was doing this to my truck, I had all the specs for the dimmer resistance and such but it was so long ago, I've forgotten. If you find to have the same problem and want a range of dimming capabilities, to keep with a stock look you could hide the potentiometer somewhere like in the ashtray or such.
I've never had or heard of a problem with heat and resistors. Capacitors and voltage regulators, yes. If you do find it to be a problem, you could get yourself a project box to place a board in with your resistor(s) on it and get yourself a small heatsink.
As for the blacklight look, lsdiodes.com carries a UV LED. I received a couple freebies with an order I placed but have never used them. I found that the blue LED puts a nice glow on the whites of my needles. Of course, the pics I have don't do it an ounce of justice. It looks sweet in person.