Scale length/nut width?

I don't know if they "should" affect you, but they do have an effect.

The shorter scale will affect tone cuz of the slightly lower string tension and the thinner nut will affect tone because of less mass on the neck.  Also, the thinner nut will affect playability one way or the other, depending what a person like more.

My best advice would be to A/B test, side by side, more than once, a couple of Seagulls each with the different neck and scale length.  Play you're favorite stuff so you don't have think too much about what you're playing and pay real close attention to the differences in sound and playability between the 2 different necks and see which one you like better. 

I've noticed over the years I'm mainly a 1.75" to 1.8" nut guy.  Although a couple of Taylors I've played are softening me up on that, just because they seem to make their thin nut necks with "more space" than most, if that makes any sense.  lol.    But ya, I need that extra space at the nut for playability.  Thin nuts drive me......well.......nuts.  he he    

I don't think the width of the nut will have any affect on the sound, only on the playability, more room to be a little off on finger placement and still have all the notes ring clearly without muting. The shorter scale length will affect volume, because of the lower string tension, less force pushing down on the bridge driving the top.

For fingerstyle, wide nut (1.75" - 1.80") and short scale (28.5") are preferred.

The other factor in nut width is string spacing. A 1.75" - 1.80" nut will have 1.44" to 1.50" string spacing (E to e, center to center). I can't think of a reason why anyone would want tight string spacing. The older Yamaha's have very tight string spacing, both at the nut and the saddle. I've seen as tight as 1.35", that's tight! A 1.69" nut will usually have a 1.38" string spacing.