I bought the Nina and Pinta, and built the latter, quite a long time ago - when Heller ship kits were being sold for the first time in the U.S., under the Minicraft label (the mid- to late sixties, I think). I think the terms "fair" and "quite decent" are pretty accurate. These kits obviously can't be expected to come up to modern standards. The "wood grain" detail is indeed pretty coarse; Heller in those early days wasn't trying to reproduce actual wood grain (with knots, etc.), but simply making scratches in the molds to keep the parts from looking smooth. I remember being pretty happy with the Pinta I built - after I dressed it up a bit with aftermarket deadeyes, crew figures, etc.
The Nina and Pinta kits use the same hull, with different upper bulwark components to make the finished models look different from each other. Since we know so little about the real ships, either one of the Heller kits, considered individually, looks pretty believable. I'm not sure, though, that I'd be comfortable displaying the two of them side-by-side, thereby making the identical hulls obvious. We don't know much about Columbus's ships, but it's a safe assumption that two of them didn't have identical hull lines.
I haven't built or bought the Heller Santa Maria kit, but I've looked at it - though not recently. My general impression is that it's on about the same standard as the other two. I built the grand old Revell Santa Maria (vintage 1957) when it was brand new - and several times later. My impression is that the Heller kit isn't significantly better - or worse - than the Revell version.
Incidentally, Heller re-used that Santa Maria hull several times as the basis of other kits, each of them more ridiculous looking than the last. Heller, of course, was notorious for such stunts.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.