As long as you digitize your home movies to DV AVI type 2 with 16bit 48khz sound you should do fine with either product
Do be aware that PPro CS5 requires a 64bit computer and OS (I use Win7 64bit Pro with CS5)
Also be aware that PreElements 9 "should" be out in the next couple months, so you might want to wait to buy
For me, the difference is great enough to justify the expense, but that is a decision that you will need to make.
Based on the outline of your Project, I kind of doubt that it would be, but let me try to outline some of the pluses and minuses between the two programs. This will be rough, as I do not have a full feature list of each NLE program in front of me, and much will be predicated on how I use each program. This will also be based on PrPro CS5 and PrE 8. None of us knows what PrE 9 might bring.
PrPro offers Sequences, which are like mini-Projects under the umbrella of a master Project. PrE does not allow for this, but most do not really need the Sequences, as the single Project works well for them, and there are simple workarounds, if one wishes to burn a DVD/BD from multiple PrE Projects. For me, the ability to edit my "chapters/scenes" as separate Sequences is very important. I have one Project with 24 Sequences, which are the "chapters" in a family history. I do the same thing with most Projects. For many, PrE would still work fine, but for that big one, I would not want to give up my Sequences for anything, as it keeps me totally organized, and that is important, as I know none of the history of this family, or even any of the family members. One benefit of Sequences is that they can be setup for different source material, so that one can easily edit AVCHD along with HDV, or even RED footage, all in the same Project.
PrPro offers true Multi-cam editing, and that is a bit tougher in PrE.
PrPro has just added Presets for DSLR cameras, but I suspect that PrE will in the next version.
PrPro offers the Desktop Preset, which allows one to customize most attributes in a Preset. One has to write such custom Presets for PrE.
PrPro now offers the ability to just drag source footage to the New Icon, and the program will automatically write the necessary Sequence Preset and set it up, ready to go.
Import of source footage is very similar, but PrPro has more pro-level capabilities, like RED footage.
PrPro is ONLY 64-bit, so it is now quite fast, and will not run on a 32-bit OS - only 64-bit. PrE is a 32-bit app., and will run well on either a 32-bit, or 64-bit OS.
PrPro has more professional Effects than PrE, but many more "mainstream" Effects exist in each program. Transitions are almost the same. Some of PrE's Effects are Auto, while there is almost always a "manual" version too in PrPro.
PrPro has more Audio Effects, than does PrE. Also, PrPro will Export to DD 5.1 SS, but that does require an optional US$ 250 plug-in encoder from Minnetonka, the SurCode encoder. Both can Import and edit DD 5.1 SS, but PrE is limited to just 2-channel Audio Export, like PrPro without that optional plug-in.
There are more 3rd party plug-ins for PrPro, but then PrE comes with some that PrPro does not, like the NewBlueFX.
Much more is done by Presets, like Title animation, and even the application of Transitions, in PrE. In PrPro, almost everything is done by hand. That is the same as with the DVD/BD authoring app. Encore, but I'll cover that in a moment.
The views in PrE are a bit more limited, than in PrPro, where almost everything can be completely customized. Now, PrE allows some GUI customization, just not as much as with PrPro.
PrPro allows Track Locking, and can easily turn-on/off visibility, or can Mute an Audio Track from the Timeline. With PrE, one can do the Mute, but should do so from the Audio Mixer.
With DVD/BD authoring, PrE does things in a semi-automatic way. It is simple to do, and there are many graphic elements in the way of Menu Sets, but the authoring capabilities are limited. That is the trade-off for that semi-automation. PrPro cannot author a DVD/BD, but ships with a great program for that task, Encore. It is fully manual - you have to do everything by hand - zero automation, but it is extremely powerful. Many PrE users, who migrate to PrPro and Encore, really hate having to do even the most simple things by hand. OTOH, I like the ultimate control that Encore provides, and would never give it up.
In the end, it boils down to ease of use for common editing tasks with PrE, but one sacrifices the additional power of PrPro. However, if one does not need that extra power and flexibility, they have just spent money that will not give much of a ROI (Return on Investment).
Now, if your Video footage is highly mixed, then PrPro would be the better way to go. If it's miniDV tape, then PrE will do a fine job with it (plus many other formats too, but mixing them can be a real issue).
There are other features, but I'm not sure if any of those would figure into things here.
Hope that this helps your decision,
You just type faster than I do!!!
PS - I just got my PrPro CS5 Production Premium, so all I need now is that new workstation. It's always something...