If you love photographing, then the purchase of newer equipment is always 'worth the splurge' (as you so nicely put it). If you don't persue your dreams, your aspirations, you'll never be any better or ever be where you want to be in life. With that said, let me do my best to help you with this.
1st thing I noticed was the coloring was off on all photos. use the below technique for producing great color corrections in a short time frame...
a. Open image in photoshop
b. Go to the layers palette and click on the half-white/half-black circle icon to bring up the Create new Adjustment Layer pop up menu. Choose threshold
c. When the Threshold dialog appears, rag the threshold lever slider under the histrogram all the way to the left (your photo will go white). Drag teh slider slowly to the right and some of your photo will begin to reappera. (this is the darkest part of your image) Click on Ok once that part has appeared.
d. Click and hold on the Eyedropper tool and choose the Color Sampler tool. Click with this tool once on the area that is the darkest. (a target cursor will appear)
e. Double click on the Threshold layer again (the gradient not the mask) and slide the slider all the way to the right. Slowly drag it to the left until part of your image appears. This is the lightest part of your photo. Press OK.
f. Click the Color sampler tool just once on the brightest spot in your photo
g. Delete the threshold layer.
h. Press CTRL + M to bring up your layers pallette
i. Select the shadow eyedropper tool in the layers palette (the one half filled with black). Move your cursor directly to the No. 1 target and click
j. Next select the highlight eyedropper tool in the layers palette (the one filled with white). Move your cursor to the No. 2 target and click.
--- There, you've just reassigned the values and immensly improved your color. If you had problem with this email me (chris@wise-photos.net) and I'll send you a picture tutorial.
Now onto the photo critique.
puertomadero.jpg :: The patterns of lines are quite nice creating a nice symetrical image. I think you coulda done without the high rise in the background as it looks distorted (no biggy, a problem with some cameras called keystoning). Plus I don't believe it adds to the photo at all.
puentedelamujer.jpg :: It's nice. However, the perpendicular lines at first confuses the eyes. It would have been better to show less of the rail and more of the white structur, making the structure more dominant looking. (possibly a lower angle woulda been very nice here).
alvear.jpg :: I dunno. Nothing spectacular or interesting really. It's the corner of a building. What set's photographers apart from one another is their style. Something that's unique to themselves. I've seen that same photograph hundreds of times but of different building. I would suggest to get more of the predominant building into the shot and have the building come to a point more towards the right of the photo.
almuerzo.jpg :: It's just a photograph. Again, nothing sticks out. There are whole professions dedicated to photographing food and restaurant scenes.
Lighting plays a major factor in all photographs. It's what will truly make or break a photograph. The best compositional photograph in the world will be thrown away in a heartbeat if it doesn't have the right lighting. Let me reccomend some books for you...
Art and Attitude of Commercial Photography
http://www.amazon.com/gp/product/0817433090/qid=1149402776/sr=2-2/ref=pd_bbs_b_2_2/103-2374003-3431006?s=books&v=glance&n=283155
The Focal Handbook of Commercial Photography
http://www.amazon.com/gp/product/0240802144/qid=1149402776/sr=2-3/ref=pd_bbs_b_2_3/103-2374003-3431006?s=books&v=glance&n=283155
Professional Architectural Photography
http://www.amazon.com/gp/product/0240516729/qid=1149402842/sr=2-1/ref=pd_bbs_b_2_1/103-2374003-3431006?s=books&v=glance&n=283155
How to Photograph Buildings and Interiors
http://www.amazon.com/gp/product/1568983239/qid=1149402842/sr=2-2/ref=pd_bbs_b_2_2/103-2374003-3431006?s=books&v=glance&n=283155
I know you may not want to do this on a professional level, but these books will help you out quite a bit.