You asked whether or not it was worth it to make an Alger. As an owner of a completed version of what you've described, I have a unique perspective.
First, let's address value when it's time to sell. It is virtually impossible to complete this process and resell the finishd product for a profit. Even assuming that your sister has all the mechanical and engineering ability to do all the work herself (or has somemone willing and able to donate these services), the money put into it will almost certainly exceed the sale price. Of course if she has unlimited resources and/or wants to keep it forever, this isn't as much of a concern.
Second, we need to know what her intentions are with the vehicle. If she wants a car that she can take to shows, parades, cruise nights, and the occassional pleasure drive, it would do well. If she thinks that she wants it to be a daily driver, or if she's just going to shut it in the garage, it would not be worth it.
Third, we need to know her patience level. A good rule of thumb is to figure out how much you think the project will cost and take, then double the cost figure and triple the time. Also, understand that, while we love our suppliers, the list of parts that are no longer available grows every year. Because the Alpine and Tiger originally sold in relatively small volumes, there are relatively few of us that are seeking to buy parts, compared with Camero or Mustang owners, so there is a correspondingly smaller parts availability.
I'm not trying to discourage your sister from taking on this project. I'll cheer every step of the way if she decides to pursue it. The reality is that for every completed project, there's another project that was abandoned part-way through.
I understand having a sentimental attachment to a vehicle becuase of a family connection. Just make sure that she has the time, money, and patience to commit to the project before undertaking it. If you would like to talk to my builder, I'd be happy to give you his number. Just email me at pmenhusen at stateexchange dot net. I also have a list of all the companies and individuals that supplied parts, which I would be happy to share.
Also, make sure that the title can be transfered into your sister's name. Don't spend a dime on the project until you're sure you can get clear title.
Best wishes