I am 5'2.5", 28.5 inseam so VERY close to you.
WSD is in theory a shorter top tube to accomodate our shorter torsos. They usually do things like smaller bars, shorter cranks, women's saddle. Here is my answers.
1.) i am drawn to the idea of a womens specific bike, but unsure whether it actually makes a difference. Depends some companies don't do alot of changes, some people who are the picture of WSD (me) don't like them. I rode a Safire (Specialized WSD) and I felt squished, I felt like I was headed to endo everytime. I used to have Gary Fisher WSD and loved it. I personally like Specialized's "unisex design.
2.) I am drawn to the idea of a 29er, but i've heard that for a smaller frame size, it might not be the best idea They have drastically improved their building of small 29ers. Two years ago I would have agreed, now I completely disagree with anyone saying us short riders can't have big wheels. I LOVE my Epic 29er, all 15.5 inches of her. I do like how fast 29ers feel, they make things smoother, anything technical they really make me more confident on. I do not believe your height limits you from trying one.
3.) if it were me, and you could pick either trek or specialized, what would you pick? any specific bikes? I have found Specialized backs their products better, it may be we have an awesome local rep but my husband had a few warranty issues on his new bike and they replaced parts no questions asked. They even warranteed his two year old shoes (technically out of warranty) because they felt the peeling sole was still a warranty issue. Plus I LOVE my Epic 29er but it is a little at the top of your price. I have ridden the Stumpjumper Hardtail and it is really fun. Full suspension will have more parts to maintain but be a more comfortable ride. Hardtail on a 29er if you don't have overly rock or huge roots may be just as comfortable. I have never riden any current Trek models so I can't speak for them.
Standover height was a huge worry for me until I tested (on trail) a couple small 29ers. I was told time and again standover was not a huge factor in mountain biking but I never believed it. I would advocate test riding on a trail if possible to see what you like.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan