Change training aircraft? C172* vs. PA28-*

Hi,

I am just finishing solo phase and have a long journey ahead. My
training waypoints are (god willing!) Private, IFR, and perhaps
Commercial and even CFI if I can keep building the skills and financing
the habit long enough to get on the other side of the checkbook.

Bottom line for now is that I am fast realizing the costs of getting
started and I wonder if it might be more efficient to switch from the
C172SP, which I love, but it is a little price; to a PA28-161 or 181.
The wet rates are generally quite a bit lower, at least at my home base,
and a couple of CFI's have mentioned that you can get more bang for your
buck in these airplanes.

For example, I've read:
---
What is your favorite aircraft to instruct in?
Reliable, and forgiving aircraft. Basic trainers a C-152, C172,
PA28-161, PA28-181. Remember the best combination for learning: Newer
aircraft and more experienced instructor. Older aircraft and newer
instructors are both riskier, in general.

What are your aircraft recommendations for a new student?
My own perspective: C-152 -- money saver(if your weigh less than
160lbs); PA28-161 or 181 -- least hours to get your Private Pilot
Certificate; C-172SP -- pricey, but new and nicely equipped; SR22 --
more expensive, but you get cutting edge technology and performance.
---

I have always had a fascination for low-wing airplanes, but what is the
consensus about a student switching during the post-solo, pre-cross
country stage of training? It is certainly wisest to solo in the plane
that one learns to fly sufficiently well to pass the solo phase checks;
however, I want to maximize the number of hours I am able to fly while
keeping costs reasonable, moving forward. Will I truly get more mileage
for my training dollar by changing now?

It would also be nice to learn the contemporary avionics at the same
time, which is one huge advantage of the 172SP's I have been flying.
The questions are, can these objectives be better (more cost
effectively) achieved in a 161 or 181? What are your thoughts on
cross-training or changing airplanes after solo but prior to that first
private certificate? Of course, if changing now would diminish the
development of the most proficient skills, it would not be worth any
cost savings, but I thought I would ask what others think before moving
forward from here.

Thank you in advance for any advice that you might have time to share.