No buyer's remorse for that setup. Always keep in mind that the camera and lens is a means to an end, not an end in and of itself. As you point out at the end of your post, with experience and an artistic eye, you will make compelling photos regardless of your tools.
To add to what BF_Hammer said:
One of the best tools for improving your photography is to look outside the medium at other art forms. Find your local art museums and become a regular. If you can, pick up some books of the Dutch Masters. Rembrandt and Vermeer made amazing use of light. Pick up coffee table books of landscapes, the impressionists, and yeah, photography books. Mark the ones that really catch your eye, and then start picking apart why they do.
Paintings and photos really benefit if they have one clear subject. This ties into what BF_Hammer was saying about backgrounds. If the background is drawing the eye more than the foreground, the background had better be the subject of the photograph. (This is typical with landscape photography: by having a clear foreground object that ties the viewer into the more distant landscape, their eye is drawn into the frame as a whole.) If the subject is the foreground object, the background needs to draw the viewer's eye back to the foreground. Strong leading lines in the background can be used this way, but be careful not to over-emphasize the role of the background at the expense of the subject.
The eye is drawn toward bright things. If there are bright patches in the background, the viewer will look at them. Rembrandt and Vermeer both used this by making the subject lighter and the rest of the scene more muted. Your last photo, of the big butterfly valve, uses this, too. (And it works!) But this is also why the photo of the sun through the trees has issues with the buildings in the background. They're competing with the subject. (Just for grins, try cropping that photo tighter on the sun and the trees, omitting the background buildings and sky. Put the sun off-center and see what it looks like.)
The eye is also drawn toward the things that are in sharpest focus. One of the reasons why portrait photographers tend to use fast primes is that they can shoot wide open and blur out everything except the subject. If you look closely at a bunch of portraits, you'll almost always find one or both eyes are in tack-sharp focus. The tip of the subject's nose can go soft so long as the eyes are sharp. The effect is to draw the viewer in and invite them to focus on the subject's eyes.
Back to the topic of leading lines, when photographing someone in profile (as in the case of your macaw), viewers tend to be drawn to the subject's eyes, then in the direction the subject is looking. (The macaw is looking at the camera, but viewers will still move their eyes in the direction the macaw is facing.) If that faces back into the frame, the viewer is more likely to keep looking at the photograph. If it leads out of frame, they tend to move on. As weird as this may sound, it's common fare with portraiture and with magazine cover shots. Just as an exercise, try cropping out the left side of the macaw shot, keeping the bird and everything to the right of it. Turn it into a vertical. (And then see the bright spots in the background. BF_Hammer is right on the money about paying attention to backgrounds. They make or break a photo.)
Try the same editing technique on the tree trunk and ivy. Crop out the left side of the frame, bisecting the tree trunk and using it to form a border on the left side of the image. Keep the ivy completely in the frame. Turn it into a vertical. The sunlight on the leaves is brighter than the highlights in the background. See how it works and if you like it more or less than the original.
If your main draw is automotive photography, the same things I said earlier about drawing inspiration from other sources applies. Pull up ad copy for high end cars. Lamborghini is particularly careful with their ad photography. Most of them are shot as a quarter view (showing side plus front or side plus rear), and have very clean backgrounds. In the instances where the background is lighter than the foreground, it's almost always offset by being a different texture, tonality, or color than the foreground car. Lots of info out there on automotive photography, and lots of material to draw inspiration from.
Find what you like, try to do what you find. Along the way you'll come up with new ideas you'll want to play with. Do it. Find what works and what doesn't. Keep using what works, discard what doesn't or figure out why it doesn't work and try again with fresh eyes.
When evaluating your own work, try to be your own harshest critic. Back when I was shooting film, I tried to find the best photo out of a single piece of film. For 35mm, that meant one in every 36 shots. With digital, I try to pick the best photo of the day. Try to understand why that one photo made the cut, and when you go back out put more of that into what you do the next day. Then cull just as ruthlessly. Wash, rinse, repeat. It hurts like hell to kill your darlings this way, but you will improve rapidly.
I've probably rambled about as long as I should on this subject. One last tip: If you ever get discouraged, screw all the advice anyone gave you (especially me!), grab your camera and one lens, leave the rest behind and just get out and do photography for the sheer joy of it. In the end that's what will keep you going. Never lose sight of it.