Answer is - depends. This isn't a question that can be answered with a simple yes or no. Given you asked that question, i assume you want to absolutely maximize your gain. Whether it's a good diea or not depends on quite a lot of factors, which more often than not closely connect to each other.

1) what's inside the fukurokumaru?

Fukus, while often at first glance different from each other only by ninjas in it usually contain different items. Some have more potions, refines, keys, other stuff. Also there are different milestones (0.5, 1, 3, 5, 8, 10, 15, 20, 25, 30, 40) dependin on each iteration. You can evaluate the value of fuku by adding the total value of items (rough estimate) in each tier. Some items, even though they might have paper value have no value for you at all when you max certain feature or you dont need frags. This drastically drops the value of fuku.

2) what ninjas do you have?

Your main pvp team, team for dailies, team for gnw and spacetime if you participate, team for events like matsurii and swb. You dont always use the same team (pvp/spacetime should have the priority to win no matter how long it takes, while swb should also be fairly quick for farming). Dailies usually consist of hiruzen/tendo/kimimaro or some r1 aoe nuke. If fuku can help you obtain missing units, it might be worth considering even if other factors arent neccessarily met.

3) what ninjas do you need?

Pretty much end of the upper paragraph. Most teams have their core member and supporting ninjas that can be replaced with a higher tier unit. If you can get frags from events or fuku of upgrades to your team, consider it.

4) what are you looking for (power or ninjas)

Straight forward. If you already have a good team, a team that has reached its full potential or is simply too expensive to upgrade (think: only upgrade worth considering is replacing an unit with bt edo hashi or bt 10t madara in the future), then consider tunneling on power and dont pay attention to ninjas at all.

5) what are the events currently on?

There might be a great fuku but with god awful events. Or good events, but bad redeemables. Eg. great plates is a good event in general, but drops the value once you dont need any of ninja frags from the wheel or the pack. Effectively the only value from it is some power items from the wheel, which suddenly makes it not so interesting, especially when you dont need adv protection vials. Same concept applies to every event. Evaluate if it gives you good value, if it gives some sort of currency- if redeemables are good.

6) what are the redeemables of current events (if applicable)?

Extension of previous point, if you have bad events with good redeemables (things you are looking for or high end upgrades) you might consider getting them regardless of fuku. I'd get my missing frags in a heartbeat regardless of fuku, if they were to be found.

If events are good, redeemables (frags or power options) are bad, then you need to think whether pros outweight the cons.

7) will getting full value of current events and fuku actually impact your gameplay in any (more) serious way?

Usually making full fuku means getting full ninja (or going 3->4* allowing bt). If it helps you finish/push hiher ninja exams, makes your team noticeably stronger and elevate your pvp capabilities, by all means that's a great time to spend your resources.

8) what's your cp average cp income / how often you are able to make a full fuku.

If you have limited resources, dont recharge, then you should really take your time to consider whether it's worth it or if you should wait. If you actually recharge quite a lot and making 20k+/month isn't an issue, you could ignore all the above, since you will be able to participate in this and next fuku regardless.

Generally full fuku makes a great deal frag wise, especially if there are good events with good redeemables. But if you can reach a milestone to recruit or 4* ninja without making a full commitment (especially when events are less than optimal), it's ok to spend jsut this required ammount (or even not reaching the milestone in fuku if you get missing parts elsewhere).

Usually lower tier milestones offer power options like pots, which are most impactful for majority. If you dont need ninjas, you might do some of fuku milestones just to get additional power boost, assuming you dont need anything else.