Jon
To be honest, I don't see any significant difference between the two plots. Through 30 MHz generally, and certainly below 10 MHz, the absolute strength of the received signal has no importance whatsoever for reception quality. What determines the received signal readability is the signal to noise ratio.
A preamp, in most cases, makes no difference either. A preamp increases the signal and the noise together and does nothing to improve signal to noise. It may, in fact, reduce signal to noise because it is one more gain stage that is susceptible to overload and intermodulation.
If the noise level in your receiver increases when you attach the antenna then there is nothing your can do at the receive side to improve signal to noise.
If you feel better about it then by all means use it. Just understand that relative signal level in and of itself is immaterial. The only thing that matters is signal to noise.
WA8TOD
Warren Allgyer