I think a kellet (or sentinel) can really help. Especially when using a short scope on a mostly nylon rode .
If I am forced to shorten my scope (re: limited swing in crowded anchorage). Then I always think its worth it and it has worked for me and made me sleep better at night. I think almost anything could be used as a kellet and you needn''t pay alot of money for a fancy one. You could just get a small mushroom anchor and a carinber Hook to attach to your rode (and a retreival line).
I like to get the kellet about half way down the rode, which also helps dampen the boat from "surging" due to swells if you get them. Further down might help more with regards to keeping the anchor shaft horizontal.
Take a look here for some technical information about the catenary effects and keeping the anchor in.
And here is a manufacturer of Kellets (Sentinals) with some info. Personally I would just get a 20lb mushroom anchor if needed.