Is it a good idea to connect data points on a plot to increase readability in slides?
Drawing the lines implies a continuous relationship between the parameters. So if you can expect continuity, then connecting the points is fine. A second point to make is to avoid colours that are as similar as the green and blue you have chosen. One reason the difference is hard to see in the first scatter plot is due to colour. Try to experiment with colours that contrast better and your problem may be solved by just altering colours for one or both of the data sets.