Hi Draythor, as a budding Pro-Am myself I thought i'd pitch in as well,
Most of your pics follow the rule of thirds anyway, but I picked up on the tree not following it,
have a read here
http://digital-photography-school.com/rule-of-thirds
I think if your tree was to one side it would have set the picture very nicely, similar to the HPIM2454 pic, it does make a difference.
The Alcatraz are good, but might be worth doing some experimenting with some nice and contrasty black and white filtering as the buildings are derelict there could be some nice moody tones to set the scene
You don't need an SLR just to take a good pic, even with the most advanced SLR, badly composed pictures can be taken, they don't improve that!!
I myself have a Nikon P5100 for when I just can't carry my D60 around, the P5100 is a compact camera but you have the option to treat it like an SLR with the amount of manual control it gives.
Im starting to get into Astrophotography now and it has it's own set of complications to achieve a picture
Here's one of my shots, using 110 8 second exposures stacked and aligned to enhance the brightness of the stars.
I'm a complete beginner at it and you can spend hours and hours taking hundreds of shots just for the final image not to work how you expected.
Anyway, keep taking the pics, you'll never finish learning