In terms of gameplay, Charizard and Alakazam were lacking in power compared to Blastoise and even cards like Electabuzz and Hitmonchan. Blastoise had the means to pump up water pokemon to use powerful attacks, and Hitmonchan and Electabuzz would whittle your HP down turn by turn. Also Blastoise would always defeat Charizard due to weakness, and Charizard's slow-as-hell attack needs.
In terms of value, Charizard is still the most expensive solely because it's Charizard. I don't see it as much today, but the mere mention of Charizard made kids go berserk back in the day.
Blastoise is second because it has value in throwback decks. And coz it's blastoise.
Alakazam was the second most valuable card at the time, but the other 2 are worth more for the aforementioned reasons.