Both of the models you are considering will do fine for your intended purposes. Regardless of what you buy, there will always be a better camera and lens than the one you have. Even if there isn't one now, there will be one soon! The most important ingredient in a photograph is the skill and experience of the photographer. Even when it comes to hardware, the camera body is, more often than not, not the most important piece of the puzzle. With product photography the quality of light illuminating the subject and how it is modified is the primary hardware concern. With landscape photography the most critical aspect in terms of hardware is normally lens performance.
The most significant difference between the two is in the sensors. The D3200 has higher resolution (24.2MO vs. 18MP). This can be an advantage at times as it gives you a little more room to produce very large prints and also to crop images. It also means larger file sizes per image which may or may not be an issue for you. The higher resolution comes at a price, though. Since the sensors are roughly the same size the pixels are packed in tighter on the D3200. This means each individual pixel is slightly smaller than the pixels on the 600D. Pixel size affects things like the Diffraction Limited Aperture, light sensitivity, and image noise. Sensitivity and noise are especially important at higher ISO. In general most reviewers who have compared the two feel the 600D controls noise better than the D3200 at ISO 800 and above. There are other, more technical reviews that give the nod to the D3200 (most notably DxO Mark, which can be considered controversial by some.)
Comparing the output of either camera in the camera store is not a good way to decide this. Perhaps the difference you see is related more to the particular settings of each camera at the time, and it is certainly concerned with the quality of each camera's preview screen as much as it is with the quality of the actual image stored on the memory card. Would you rather have the image that looks best on a calibrated monitor or the one that looks best on the back of the camera? Screens on the back of cameras are known for not being very accurate in terms of color, especially under lighting like you find in most retail establishments.
If your images are going to be viewed primarily over the internet, then either camera has more than enough image quality to produce excellent photos. Choose one and start learning how to use it!