Honestly it really depends on your intention as to why you want to sell your HDB. If there is no reason selling, then no point. Just keep your HDB. But if you want to upgrade to condo, then maybe. Probably you can take a look at this blog article https://www.hdbupgradingstrategist.com/should-i-sell-my-hdb-and-buy-condo/

Hope it helps...