So you are technically looking for an "every-green" niche. There are two most known ever green niches: health, wealth and romance which will never die.
And about your question, if you asked this question 10 or 15 years ago, the answer was different but for now and today, I would say it's better to focus on the past 5 years since we are living in a digital age. When you analyze the trends of the 5 years ago, you will be able to know the market demands, customer behaviors, and technologies used much better than 1990s because you have access to more data.
Also,although the 1990s has some nostalgic value but if you look at this from point of a business, in general, audiences are more interested in current tech, trends, social media as well as digital products rather than things that can exceed their expectations of 1990s. So my advise is to focus on the past 5 years to find your winning product.