[Wavytone]

One eyepiece won't really do it all and Barlows are a fairly inferior solution to buying a really decent high-power eyepiece.

First what's the focal ratio of the Dob ? With a short focal ratio newtonian, (at a guess I suspect yours is f/4 or 5) spending a lot on low power eyepieces is misguided because over a wide field (say 30mm or more diameter at the field stop) your scope will have heaps of coma and field curvature degrading much of the field of view, unless you add a corrector that flattens the field and fixes the coma. As you already know your 32mm is useless, probably for this reason, as will be most other long eyepieces.

Where the $ would be useful is a good eyepiece round the 10-15mm mark which when barlowed will give you 4-5mm depending on which Barlow you think is any good.

If you really find you can use 4mm a lot then maybe one day buy one, but I think that is unlikely.