Thanks everyone for your comments on my previous post!  In the light of a new day I thought I'd give you the run-down on the how and why for the changes I made to the top half of the 'ruffle-less Spring Ruffle Top'.

From the outset, can I say that these changes in no way reflect a deficiency in Rae's original design.  I really liked the look of this top from the tutorial, but I'm not much into ruffles, and did like the 'ruffle-less' versions better than the original.  The changes were really as a result of this preference.

I planned from the outset to make two tops, and I cut the rectangles for the top of the bodice as per the instructions as a first step.  I sewed the top band, ironed the straps as instructed and pinned on the front of the straps.  I then had the Cyclist pin the back straps for me, with the instruction to cover my bra straps with the straps of the top (I hate having them show).  What I noticed was that:

• Even though they looked right to the naked eye (as far as I could tell looking over my shoulder in the mirror any way!), they weren't lined up properly.  You can see this on the photo below.
• The straps weren't wide enough to cover up the structure of my maternity bra unless I added the ruffle,
• The horizontal strap gaped a bit at the underarm seam, and would fit better if it was a little narrower at the top than the bottom.

I also decided that I'd like to add a bit of a curve to the neckline, because I plan to make both of the tops with a white top half, and thought that some difference between them would be nice.  The result was that I used the straps to draft myself a 'bodice top' pattern.  Here's how I did it:

I traced the outline of the front onto tracing paper.  I also traced the back, but instead of only tracing the back half of the straps, I traced around both the front and back straps, so that the strap section was wider at the bottom - I figured that this and the curve I was adding at the underarm would cover my bra sufficiently.  I took care to mark where the original fabric was folded, as I would need to add seam allowance to these pieces.

Back pattern piece

I then folded the front in half, and made sure that the pattern piece was symmetrical.  Where it wasn't I adjusted it to the mid-point between each side, and thickened up the lines.

I then added in the curves.

I did the same to the back, also making sure that the straps for the front and back were the same distance apart at the shoulder.

Back pattern piece on top of front pattern piece (both folded)

I cut two of each piece, so that the bodice was fully lined, adding a 1.5cm seam allowance where I'd marked the need to do so on the pattern.

I didn't worry about sloping the side seams on the pattern, I just stitched them on an angle (my seam allowance was 1.5cm at the underarm and 1.0cm at the bottom of the bodice piece).

To sew, I sewed along the necklines and underarm/outside strap seams (pinned on the photo below).  Next I joined the side seams.  Lastly, I folded the seam allowance on the back straps inside at the shoulder, slotted the front straps into the back straps, and topstitched in place.

In hindsight, an added bonus of this approach is that I'll be able to use some of Grandma's ric-rac on the neck and armhole edges of the second top (strange that I've not used any of the trim in the 20+ years I've had it, and now I'm thinking of using two different colours within a week!).