Late to the party here, but i'll suggest that IS is almost always worth it on a guard if you anticipate using the guard in the SG and occasionally the SF position. 1v1 @ FW for 5-6 weeks will get a pop in Is most of the time, and the necessity of 9-11 IS can be seen in the average shot selection of players. You could make the same case for ID. if a player has great IS and ID at SG, they'll defend the opposition for between 10-20% of their shots that end inside and take those shots rather effectively. Maybe 55% make and defending 80% successfully. If there are 4-6 inside shots, it's probably a swing of 4-6 points. Sounds like relatively little, but it's the difference between 21 PPG and 26 PPG at SG and perhaps a similar result at SF and PF. Centers and PG's are less impactful because of their amount of shots per game, could be 0-2 points impact.
This is why you will see 6'0" guards on the market that are low in their secondary skills go for cheaper than expected sometimes. i'd say about 40-50% of longterm players of buzzerbeater will target higher secondaries because they value not having to train them as long.