I came across this when I was doing some research for my recent pumpkin stout...
(The True Story of the First Pumpkin Beer!)
Pumpkin Beer « Beer and Food
And to disagree some, while a historical 'pumpkin ale' may not have traditionally used cinnamon, mace, ginger, cloves... in the form as we know it, we do know that such spices were used in colonial brewing. There are many colonial recipes for ginger beers, spiced hard ciders, spiced metheglin, and other brews that utilize the same spices found in our modern pumpkin ale - and the association between pumpkin and 'pumpkin spices' was well established since the 17th century. Various recipes exist for pumpkin puddings, pies, and torts exist that use said spices - including a recipe from the first American cookbook (by Amelia Simmons).
Therefore, while we do not have a historical 'spiced' pumpkin ale that fits our own style, I believe it is rather foolish to assume that it was only in 1985 that an ale brewed with pumpkin and spices was made. The colonial association between such spices and pumpkin was well established and such spices were already being used in other fermented beverages.
I'm afraid I must respectfully disagree.
Nothing you've said proves anything. Provide proof those spices were used in
beer brewing at that time in Colonial America. That ginger beer and other spiced potables existed is not evidence that spiced pumpkin beer existed. The extant recipe I quoted above, for example, lacks any mention at all of traditional pumpkin pie spices. I've never seen one that
does mention the spices, and it isn't for lack of trying!
Vegetable oil, mustard, vinegar and eggs have existed for thousands of years. That doesn't mean mayonnaise existed before 1756. Unless it can be definitively proved that traditional pumpkin pie spices were used in beer - not flip, cider or mead/metheglin, but
beer - all anyone can say is that they were not. That's the difference between fact and conjecture.
Call it foolish if you like; it was and remains responsible historiographical practice. I'd rather practice solid, academically reliable
history than haul out the tired old, "They had X, so they
must have done Y" straw man. Without proof they used X for Y, there's nothing more than conjecture. Conjecture is, without proof, a useless waste of time and bandwidth.
Lastly, while there is undoubtedly a difference between modern brews and historical ones, the difference between them is not necessarily because of a profound change in ingredients or brewing processes, but instead due to a refinement of ingredient proportions, as to fit our modern tastes and purposes.
True and not true at the same time. Even a cursory examination of the development of brewing's raw ingredients shows the profound differences between historical and modern ingredients. That said, tastes have changed also, and that has had a significant impact. For example, before Wheeler's invention of the drum roaster in 1817, brown malt was a diastatic base malt used in the brewing of porter. After 1817, the grains we know as chocolate, roasted, and most importantly black patent were invented. Make a porter with brown malt as the base and further color and flavor provided by molasses or essentia bina. It will be like no other porter you've ever tasted. Now, did that come from tastes changing or from ingredients changing? For all I know - I haven't exhaustively researched the topic - it's a chicken-egg argument.
Here is a book that may help. Ive read it a few times and its pretty interesting Beer in America: The Early Years--1587-1840: Beer's Role in the Settling of America and the Birth of a Nation: by Gregg Smith.
I've got a very tattered and dog-eared copy of Smith's book, from which I've gone on to collect most of his sources.

It's a lovely book, written in an easy-to-digest manner, and very informative. Amazon usually has it at a good price, and I've seen it on the shelf of my local B&N/Borders stores.
Bob