Advice on Nikon camera gear?

I have between $1, 000-1, 500 budget to expand my collection of camera equipment. I'm torn between buying a new body OR buying a new lens and flash equipment. Looking for advice.

Currently, I have the following:
Nikon D3000 (it's been great but I know I will want to upgrade soon. I'm considering the D7000)
Nikon DX AF-S 35mm 1:1.8g
Nikon 55-200 f/4.5-5.6 AF-S DX VR
Nikon 50mm f/1.8D AF (that I manually focus on the D3000 body)

So, here's my dilemma:

I have a lot of high quality glass (Pentax k-mounts) that i use on my film camera. I could, potentially, purchase an adaptor ring (Nikon body to Bayonet mount lens) so that I could use all of my lenses on a nikon body. Granted, the images may lose some sharpness. In this instance, I could buy the Nikon D7000 (body only) and use a great variety of lenses… But no flash.

OR

I could purchase a high quality Sigma lens (Auto Focus? On D3000 body) that is intended for portrait work, as this is the area I'm lacking a lens. The 50mm is great for portrait work--sharp-- but at times the manual focus in low light conditions is not favorable. With this instance, I could also purchase a flash.

Currently, I use my 35mm the most. I shoot architectural elements, nature, etc. I rarely do portrait work but I would like to.

Suggestions?

I'm open to many ideas.

Added (1). I'll probably sell my 55-200 anyway & put some of that money toward a different zoom lens.

Any suggestions for a zoom lens, keeping affordability in mind-- budget of $500-$600 or so. Must be capable of auto focus on d3000.

Don't bother w/ a Pentax-to-Nikon adapter. You should put your money towards a nice lens or two. I know the D3000 isn't the greatest camera out there, but since 2 out of 3 of your lenses are DX lenses, its time to get some new glass.

1. Skip the Pentax idea…
2. I went through something similar a few years ago, and upgraded my camera body because I wanted autofocus capability with more lenses. I think upgrading the camera body is a great idea, but maybe a lower priced model. The D90 is more affordable, still one of the best DSLRs you can get, and you'll have spare cash for a flash unit. In fact, I wish I did that instead! I got the D7000, and though I'm very happy with it, it's features didn't really justify the price difference for me.
3. Most photography enthusiasts recommend glass over body any day. Perhaps you should trade your 50mm D lens for the G version, then you could have AF on D3000.It would serve well as a standard portrait lens. I would also recommend the new 85mm 1.8G lens. It's $500 and is also a great length for portrait work.
4. The cheapest Nikon flash solution would be the SB400 (about $150) and you can tilt it to bounce off the ceiling. For full swivel and remote options, you'll have to get a Nikon sb600 or sb700 (over $300).

To satisfy all of your needs, trade/sell your D3000, 55-200mm lens, and maybe your 50mm D lens. Grab a D90, a 85mm 1.8G lens for portraits, and a flash unit and you're set! A better camera than the D3000 with a built in motor for AF compatibility and more lens options. All that while being able to afford a flash unit.

What is that high quality Pentax glass that you have? You don't seem to be terribly deeply invested into the Nikon world.

If your Pentax glass is worth more than your Nikon glass, then you might consider the brilliant Pentax K5.It can go toe-to-toe with the D7000.

I use a Tamron 17-50/2.8 as a standard zoom. It's far better than the kit lens and autofocuses on entry level Nikons. Perhaps that would be one for you to consider.

The non-VC version is said to be sharper, but based on my experience that's not true - the VC version is just as sharp if one gets a good copy.

The Nikkor 18-200VR is a very popular choice too.

Getting a D7000 would mean you get autofocus on your 50mm. It also blows the D3000 away on pretty much anything.

A good flash, nikon's sb-700 for example, is something you'll want sooner or later. With a D7000 you could even use it away from the camera (hint, google strobist)

Nikon also makes a 50mm f1.8 af-s that does autofocus on your D3000.It's affordable enough especially if you list your f1.8d on ebay

The pentax glass may well disappoint. Shooting film and printing 4x6 is nowhere near as demanding as modern digital sensors and a pc screen.

Sigma used to make the 50-150mm F2.8 EX DC APO HSM II which is a fine portrait zoom and it does autofocus on your D3000.