first - where do you live?
I would hardly call a GPS system "crucial" to navigation. The instrument certification usually means a few things. One, the receiver itself has been designed and thoroughly tested to meet accuracy standards that are set for IFR operations. Second, the installation of the GPS must be in accordance with approved procedures, including the antenna mounting and wiring quality. this ensures that the GPS will not only be able to receive the signal but also keep the signal, with no interference from other devices on the radio. For a VFR only installation this is not required, because you will be flying VFR. Also, the database on the GPS is kept up to date, ensuring that you can shoot approaches that are available, adn that you cannot shoot approaches that are not available. while the airports probably don't move very often, the approach procedures do occasionally.
You will want to verify with potential clubs what the useability of their VFR only GPS is. If its a garmin 430 that just has a VFR installation and an old database, you can still shoot approaches with the GPS, just not under IFR. i.e. you can use this GPS for instrument training but not for primary navigation while on an instrument flight plan.
in no case is a portable GPS approved for shooting GPS approaches or for primary navigation IFR. of course, any GPS is excellent for situational awareness. Given the choice, I would always prefer to have a GPS.
Everyone must believe in something, I believe that I will go flying.