Perhaps in hindsight, Iglesias always had a stellar tool - hand eye coordination - and what we are seeing is the actualization of that ability as a guy who puts everything in play.
And I think that gets lost in this discussion. The scouting reports on his offense, from the time he was signed on up, mentioned his quick hands and the hand-eye coordination that was evident in his defense. To say that he's outperforming expectations is to base your expectations solely on numbers - something that gets done a lot around here with young players (Visit the "Bogaerts Bat" thread from about a month ago). One of the problems with that is that he was promoted aggressively due to his glove. The statistics we have available are those along a steep learning curve. The only age-appropriate level he saw along the way was his 13 games in Lowell as a 20 year old. How predictive can his hitting stats be while he's still learning to hit in a constant state of adjustment? But, even if you base those projections solely on stats, he'd already exceeded Adam Everett's offensive output, who's been his most frequent comp that I've seen over the last 5 years. The highest OPS+ he ever achieved was 80. So, your floor has to be as a 2-3 win player through his prime. Simmons is probably his best active comp - he's been a 3-4 win player. And that's if he never translates any of the raw skills scouts identified.
An example of one of those scouting reports, from soxprospects.com:
[SIZE=8pt]Scouting Report[/SIZE]: Elite defensive skills highlighted by extremely fluid hands and soft glove. Excellent instincts and anticipation produces his well above-average range. Will get to balls that most, if not all, will not. Plus, accurate arm. Adept at throwing on the move and has outstanding body control. Future perennial Gold Glove shortstop. Grades as an "80" defensively. Can also play second and third base more than adequately. Major-league ready in the field. Plus bat speed accented by quick wrists. Low maintenance, compact swing. Little lower body in swing mechanics. Pulls ball hard, but struggles driving the ball the other way. Minimal power projection. Can evolve into a solid-average hitter for batting average and show doubles power as he matures. Small frame with not much more room to pack on muscle. Extremely impatient approach. Making strides and improving with understanding of his strike zone, but inexperienced professionally and very age advanced. Neglects to cover outer third of plate with eyes. Struggles staying back against breaking balls. Must improve with handling of off-speed stuff to hit consistently at big-league level. Above-average speed. Projects as #9 hitter in first division team's lineup, with ceiling of #2 hitter as he approaches his late-20s. Due to advanced defensive skills will most likely learn to hit at the major-league level and slowly ramp into becoming more proficient at the plate over the course of big-league career.
As to whether or not it was a good trade...I like Iggy and was/am more bullish on his value than a lot of other people on here. The Red Sox won the World Series.