Mine did that too in the summer time and we're in similar growing zones (7). I attribute it to the heat, thought I've never though much about it. Many of my oncidium alliance plants suffer from those spots. I suspect its the heat, because growths that occur during the winter (when my plants are indoors and under lights) don't develop the leaf spotting.

There's nothing you can do to get rid of the spots that are already there, aside from cutting away the leaves, but that's not a good idea. Basically, they're just cosmetic damage, the leaves are otherwise healthy and productive.

As far as the leaf tip damage, you may be letting the plant dry out a bit too much between waterings OR you might be over watering (and killing off the roots). Sounds kind of odd doesn't it?

Anyway, increasing the humidity would probably help with the spotting and leaf tip die back. I'd also suggest checking the roots to see if they are white and healthy with lots of green growing tips. If they look bad, don't worry too much, but cut back on watering for a bit and consider repotting the plant.

Personally I wouldn't divide the plant when you repot. It actually looks fairly young and there aren't all that many growths (for a Twinkle). Give a another year or two before you consider breaking it up...really let it get large and healthy unless it's completely over grown the pot. Your plant is at least another growing season or two away from that point, though.