I was talking to another line pump guy from out of my area today. Told him how I put the sponge ahead of the prime then concrete. He told me he has never used the sponge or paper wad and never has a problem. Am I wasting my time? I run 3" hose and pipe.

I usually don't use a sponge myself. as long as your primes ahead of your concrete it should be fine

The only time I will is if I'm going down hill.

And my rule of thumb is one 5 gal bucket of prime (we use bentonite) per 100' of 3" 

yeah downhill is the only thing that should require a ball. and depending on the length of the downhill its sometimes not even required.

There are a few variables for priming I guess.  The best thing to do it is think about it.  The prime is to wet your hose 360 degrees inside to keep it from sucking all the water out of the mix and plugging you up.  If your mix is real wet then a 360 might not be that important.  Going down hill does need something to hold back and wet the hose  360 or you will just wet the bottom part.  You do not want the prime to out run your mud.  I just have a line pump and run 2.5" hose 99% of the time.  Very seldom do I use anything other than water.  If I am pumping a 3 or 4" slump I will use bentonight and a paper wad.  I pumped 600' a few times with a 4" slump by pouring a slury of bentonight in the hose then placing a wad behind that.  Then my normal prime and never had a problem.  Just be carefull not to get to much prime that might mix with the mud and segrate and plug you also. Use a wad every time if you want.  All that matters is the end results, no plugs.  

i only use wadded up paper when I am on a big downhill pour , and thats not very often where I live and work , whatever works for you is what I'd say to continue doing.

It will make you even more sure of succes.. I also don't do it all the time. Mostly down hill or very long line.. But NEVER any problem is BS.. plugs just happen once in a while. Everybody has a plug sometimes. I've also heared pumpers say the never have plug but their customers tell me different