From what I've read, historians have found no conclusive, archaeological evidence that the Anglo-Saxons used ship masts in their ship design during the 5th Century. How could so many Anglo-Saxons have made such a long journey using presumably oar power alone?
I imagine that the use of Anglo-Saxon mercenaries by the late or post-Romans could have advanced the population of Anglo-Saxons in Britain, but the emigration has always been described as an invasion from across the sea, at least from what I've heard.
Is it possible that such excavations at Sutton Hoo, near Woodbridge, Suffolk only uncovered a coastal and river raiding vessel? Are there any instances of ship masts being re-used due to their value or worth, which would preclude them from burial?
I'm a bit confused by your question, though I think I might be able to answer it if you can clarify a bit. Are you arguing that the lack of archaeological evidence of masted ships in the 5th century implies that the Anglo-Saxons did not use masted ships? People living along the North Sea coasts certainly had masted ships before the 5th century and after the 5th century, so I would be wary of assuming that there was a sudden 100-year gap in use of masted ships there in the middle.
Regarding the Sutton Hoo ship, it was a similar design to other contemporary ships -- the pieces of the Gredstedbro ship (c. 610) that were discovered in southwest Jutland mirror in their structure the Sutton Hoo ship (c. 625). Two ships discovered across an ocean from one another does imply that the Sutton Hoo ship (or one of similar design) would easily be an oceangoing ship; the ship was probably 60-75 feet long and would have been quite capable of crossing the North Sea. (It is of course a 7th century ship.)
So, the short version of this is that I wouldn't read too much into the preservation (or lack thereof) of masts in any period -- we have so few ships preserved that a lack of evidence of masts certainly isn't evidence of absence.
A good resource on this is Dark Age Naval Power: A Reassessment of Frankish and Anglo-Saxon Seafaring Activity by John Haywood; the first edition was criticized for eliding or passing over some examples which didn't fit the book's narrative, but the revised edition (2006) is worth reading.