I'm not an expert on clad quarters, so I'll leave that one up to the other members here.
Does your '68-D nickel have full steps? I can see some lines, but it's hard to make out in the picture. If it has six full, strong steps, it might be worth $1-2. It is not uncommon to find exceptionally well-struck nickels from that year, but full steps are rare in all nickels until about the mid-1980s. If the steps are weak or smooth, it's worth about 10-15 cents. I'd agree that there's not much point in sending it in for grading... as a quick guess, I'd say it's MS 61-62. I'm seeing two scratches on the reverse (left central pillar, and upper-right field above the dome) and at least one small nick on the obverse... these would keep your coin away from the 65+ range that would bring a real premium and justify a grading fee. Still, it's certainly a keeper.
The gold coloring is normal toning and is pretty common on old, high grade coins. It doesn't really add or subtract value.