Kibbles Mom suggests the best option for you perhaps.
For just a one night stop and short on time (via hwy 101, it is a minimum five hour drive), Lompoc is pretty much out of the way for you as you leave the 101 to reach it.
- although nice to go and enjoy their "famous" Jalama burgers while camping overnight
- is quite small but you can get out on the beach and walk a distance.
- can have tar and seaweed along the water
- the wind can gust through there in the afternoons and the water is fairly cold (if you want to play or surf, wear a wetsuit).
- NO cell reception
- the drive off hwy 101 to Jalama Rd is about 10 minutes. Then another half hour on a 14 mile curvy and windy road.
-Lompoc is about 45 minute drive from Jalama Beach.
Unless you plan to visit Lompoc's most extensively restored mission in California with docents to guide you on the weekends, see the wine ghetto for wine tasting, or enjoy arts and murals, then enjoying the dunes and staying in Santa Maria (thus saving an additional two hours on the road just to go to Jalama beach) might be the best option. Prices for hotels in Lompoc and Santa Maria are comprable and you could get even better prices through Priceline.
Hope this helps some. :)