So which one do you want, the VHF-Hi or all band?
In any case, what you probably need is a better antenna, rather than a preamp. Either a better all-band antenna or even a tuned antenna to the frequency of the VHF-Hi band portables you are trying to monitor. Find out the exact frequency and get an antenna that is at or near that frequency. E.g., if the frequency you want is 154.8300, then you can get a VHF antenna that covers 140-170 MHz or an antenna tuned to about 154.5 MHz or even to the exact frequency. Use this antenna when your are trying to monitor those elusive VHF portables you are trying to pick up. Use the all-bander antenna for general use.
You will find that a good monitor (scanning enthusiast) has an arsenal of all-band, dual-band, tri-band, single-band, and fine-tuned antennas.
If you are at home trying to monitor, then a basic base antenna on the roof or the side of the house will make a huge difference. The same thing if you are mobile in a vehicle, a basic trunk or roof mount antenna will make a huge difference, as opposed to using the rubber duckie.