So you're still supposed to 'keep" the feasts, but not do anything that the OT meant when it said the word "keep".
How convenient.
Hebrews 9 explicitly tells us that we are under a new priesthood with Christ under the new covenant. Hebrews 10 explicitly tells us that sacrifices are needed, but that the sacrifice of Christ is sufficient.
There is, under the new covenant, a different, spiritual understanding of the feasts and their intent. Paul indicates this:
1Co 5:7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:
1Co 5:8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth
The lesson that Paul tells us about the days of unleavened bread is that leaven represents sin. We should root out sin from our lives as God commands us to root out leaven from our homes. A physical act can and does teach a spiritual lesson.
However, there is no indication that God ever wanted anyone to STOP observing his holy days completely and to START observing man made days rooted in paganism. Talk about topsy turvy! Look at what you're defending!