Scope size and type, eyepiece and magnification, as well as light pollution and seeing are some of the elements that will have a bearing on the improvements filters will make.
Whilst light pollution filters can improve what you are seeing, I've been blown away by the improvements Nebula filters make on targets like M42, Eta Carina, Trifid, Lagoon, etc.
I have 2" Lumicon OIII and DGM NPB filters mounted in a slide on an 18" dob. Whilst both vastly improve nebulosity and the ability to expose the fine detail, my preference weights strongly towards the NPB filter for nebula.
Everybodies opinion is different, and there is a great review here on the 2 filters I mention:
http://www.cloudynights.com/ubbthrea...9/Main/5919335
IMHO a H-beta filter is overkill. There are only a handful of targets like horsehead to use the filter on, and unless you have a meg dob and really dark rural skies horsehead is pretty elusive to visual observing. Whilst there are plenty in this forum that have seen Horsehead, I've only had the occasion to really try once with a 22" dob in very dark skies with a h-beta filter. Of the 6 or more of us that looked through the eyepiece, 1 or 2 said they definitely saw it, a couple thought they saw it, and a few of us said we didn't see it
For the price of a h-beta, you can pick up several other filters that you'll get more use out of.
Paul