Aftermarket seats yay or nay

From an aesthetic perspective, aftermarket seats are fine, but it needs to be a total package to reduce the cringe factor.
Original steering wheels, dash and gauge clusters, door panels etc, are all very angular and dated appearing when you introduce a modern looking seat to the package.
Scale is another factor. Most modern and aftermarket seats are significantly larger than the ones originally fitted to these cars.
The effect is that everything around those seats will look too scaled down to maintain good proportions.
But, like has been said a zillion times, it's your car...do whatever makes you happy with it, and ignore the critics