Wondering whether to upgrade amplifiers ?

Like the suggestion of the NAD Master series.  So many of us guilty of creeping up on improvements, which is understandable, but really represents false economics and oft a needless chase, unless you like that sort of thing.

Purchasing once well is much more savvy than purchasing in numerous increments.  Then we need to sell that old thing used, it's endless.

A final solution might be to consider a Sugden A21SE integrated or similar quality and be done with power for the next 15 years.

It will likely sound better. I wouldn’t worry about the upper rating of the speakers unless you actually crank it to the max. If this is a one time upgrade it will probably sound better, more solid bass… more effortlessness in the sound.

If your long term plan is to improve your system to be much higher quality, then most do in increments. Then this might be a good time to buy a separate amp instead of swapping the whole unit. If you want a really good system someday it will likely consist of a streamer and a higher quality integrated, or more probably a Streamer, DAC, preamp and amp. Generally separates perform significantly better. If you don’t think this is a route your likely to take… your choice sounds good or jumping a bit higher to NADs Master series. My rule of thumb is always at least double your investment if you want to get a “wow!” That sounds a lot better. 

In my experience yes.   Several years ago I bought a NAD 80 watt integrated and returned it for the another NAD integrated rated at 150 watt and the difference was significant.  
If you are upgrading within the same manufacturer and product family  - watts and headroom increasing is realistic