Of course they should.

There're various financial instruments enabling this very well. Simple question and Dave is totally right while Fred still lives in the past and ignores the basics of dealmaking.

The first and those who were quick in decision making should pay less than those who join later the same round. To join a full party is always a safer bet than being the first guest, so simple.

Investor's reputation/brand/name and their network are other key drivers to the prices.

There's one exception: when VCs know each other very well and brought themselves into the round/deal then their good relationship (and potential other deals running besides) will usually prevent different prices.