If you paid early on you where not just paying for alpha access you were funding the kickstarter.
Now that the game has reached Alpha stage it is no longer a kickstart. Implying they had the initial funding they needed. Please reference the concept of a kickstart.
So now that it is Alpha, and still apparently in need of more money, I would expect a lower cost of entry.
Keep in mind the simple fact of kickstarter games. You're concept and design of a game was so far off the market that no major company wanted to fund it. You had to turn to the general populace to fund your idea and get it off the ground. You now got that initial funding and want more help testing and refining said game.
At this point if you want more money your either, missed project cost projections, or enough normal folsk still don't back your idea. Now you can choose to try to make the game you want with the money you have or ask for more via alpha access.
Asking for more than the kickstart is just greed at this point as, in my opinion, you are asking others to back a flimsy or unoriginal idea at best.
Kickstarters are a good idea in theory. I worry that too many people are now abusing them as a way to make quick cash off of good will games or worse just flat out rip-offs.
Make a game worth my money or the best you can with what you have.