Welcome to the forums Robert!
I have recently started up an aeration system on my 1/4 acre pond for the first time and noticed an increase in bottom temps. From the time I started the system at 15 minutes the first day and basically doubling every day after I saw a ten degree rise after reaching 12 hours a day. The details are located in this thread...http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=495076#Post495076
I know nothing about trout, but I think you will see a rise in bottom temps and a lesser drop in surface temps (just because it is so directly affected by the sun). The intermediate waters will stay about the same or drop a little relatively speaking. BUT, you should have more D02 in the intermediate and lower waters for the fish to enjoy.
Consider only aerating at night to avoid the warm parts of the day.
How many turnovers will your system do in a day?
Spring water coming in may be cold, but spring water is usually low in oxygen.
I have read that the upper 1/3 to 1/2 of the water column is where all the usable 02 is (without aeration) and by oxygenating the lower water, it will certainly aid the fish even if the water is a tad bit warmer. Hopefully someone with trout experience will pipe up and shoot me down if necessary.