I've found the main thing is if you haven't hit $15k that year and are close just spend the extra to get the free certificate (cat 1-4).
Say you had spent $14k, so need $1k to get a certificate worth 15k, then $1k gets you 15k points, so you 2.5 points per dollar (versus 1 point per dollar).

One tip for people is not to choose the WOH milestone bonus right away, because it gives you more time to use it if you delay choosing it. Also, DSU may not always be the better option, especially as many of us have had them expire unused recently.