Have specs changed in the last 15 years?

Power has increased about 3 to 5 x and typical bass extension is a least about an octave more.

Power has become very much less expensive... 15 years ago, you could hardly find a class D amp... so yes, you will see more power today then you did then.

But that a side... do you REALLY need all that extra power? If you have a larger room and/or you usually crank the volume way up, then you might, but if not... well... you might be fine with you 15 year old Mirage... that is not a bad subwoofer at all.

There is valid reason for the big increase in the power and capabilities of modern subs. About ten years ago, Digital Dolby 5.1 and DTS movie sound began to dominate. When that happened, the bass in movie soundtracks became much more of a challenge to fully reproduce. <20hz material is not that uncommon. To do justice to sources like that, a good deal of clean power and headroom is needed. Also, if a smaller sealed sub is preferred, even more power is needed.

As Audiojan says, now, digital switching amps are pretty cheap, and work well in applications that are limited to 200 Hz and below.

As has also been suggested, 15 years ago, response down to 25Hz at 105 db was considered very good performance. Now, people are looking for 105 db at 15 Hz and greater overall output as well. This takes more amp power.