This can still be optimized (I'm out of time here). But this should be an enormous improvement.

WITH CTE AS

(

SELECT Usr,

CASE WHEN val1=1 THEN 1 END AS val1,

CASE WHEN val1=3 THEN val2+1 END AS val2,

CASE WHEN val1=0 THEN val3 END AS val3

FROM TestExecPlans

)

INSERT INTO DestTable

SELECT *,

(SELECT MIN(mv)

FROM (VALUES (val1), (val2), (val3)) AS t(mv)) AS MinSimilarity,

(SELECT MAX(mv)

FROM (VALUES (val1), (val2), (val3)) AS t(mv)) AS MaxSimilarity,

MAX(val1) OVER (PARTITION BY Usr) AS maxval

FROM CTE;