Amplifiers can work, however if not done correctly, they will not only amplify the stuff you want to hear, but also the stuff you do not want to hear, like interference.
Often an approach that works well is to look at your overall antenna system.
Using the appropriate antenna for the job:
-You say "Scanning mostly VHF", are you using a high gain VHF antenna, or something like a discone, quarter wave, etc?
-If what you want to listen to is all in the same general direction (distant city, tower site, etc.) you can sometimes do better with a directional antenna.
Antenna height:
-Getting the antenna up high so it can physically "see" what you are trying to listen to. If there is a lot of terrain in the way, buildings, etc. that can impact performance.
-Moving the antenna to a better location. With multipath distortion, sometimes moving the antenna a few feet in either direction can help.
Coax:
-Are you using good coax? All coaxial cable will have some amount of losses associated with it. Those losses go up with length and frequency. Using shorter cables, or higher grade cables, can get more signal to your radio.
-Old, weathered, deteriorated coax might need to be replaced. Coaxial cable will not last forever, and especially true it the connections were not properly weatherproofed.
Amplifiers can increase the amount of signal that gets to your radio, but there's some work that needs to go into it. You need to start with a good signal, so the right antenna will help. Ideally, you want the amplifier to have some filtering so it's only amplifying what you want to listen to, not all the other garbage out there. You also want the amp near the antenna, so it's got a good strong signal to work with, and boost that before sending it down the long coax to your radio.
You also need to power the amplifier, which will require injecting power from the radio end of the cable.
If the coax between the antenna/amplifier and your radio is in poor condition, it's not necessarily going to fix the issues.