That's a bit like trying to buy a car that can only achieve a top speed of
75 MPH to make sure you don't speed on a road with a speed limit of 75. A faster car might be a better deal because of features, price, or quality. It's up to you to control your speed.An amplifier is rated at a certain wattage based on how much RMS power it
*can* deliver without overheating or distorting. The overheating is based on continuous use, and it is unusual for music to maintain a steady volume. So an amplifier might be able to deliver short bursts of higher power without overheating. This may be what was once termed "music power". However, there are also limits determined by the power supply rails, beyond which the output will be clipped with associated distortion. Sometimes the distortion may not be objectionable, and may even sound good in a guitar amplifier. Ironically, when the output clips, the waveform approaches a square wave, and efficiency increases, so heating will actually lessen, and you can get even more power out.A speaker's power rating is based on similar criteria. A sustained note at its rated power may cause heating to a maximum safe temperature, but it could also be based on the limits of travel of the cone before it distorts or cannot move further. Short bursts of higher power might not cause thermal damage, but could inflict physical injury to the components.
Another factor to consider is that a higher power amplifier driving a lower rated speaker will have better "damping", or more linear control over the position of the voice coil because it provides a stiffer voltage source. And you can also add extra speakers in parallel, so two 75 watt speakers would be well matched to a 150 watt amp. Some speakers are fused to protect against overload. It might be a wise precaution.
Paul