As announced I went to my camera dealer on saturday and had a nice little chat with one of the salespersons. Quite some deep knowledge he had indeed.
I ended up giving back my Tamron lens (which he wasn’t surprised about) and bought a new Nikon 18-135mm lens. The new lens was about 100€ extra, but I think it’s worth the money. We’re still on the cheap end of the pricerange anyways.
I gave the lens a quick test on Sunday and must say that the focus is much more precise and faster, picture quality is somewhat better, even when looking at a downsized picture on the monitor. Just have a quick look at the shots in my new gallery.