To Di2 or not (or an expensive solution to a simple problem)

My 2 year old Lapierre Sensium 300 was due for an overhaul. The Ultegra 6700 groupset that came with the bike worked pretty flawlessly for the first 10,000 km or so of riding but even with regular maintenance, I found myself having to constantly tweak the bike to get smooth gear changes. Another new set of cables and outers alone might have done the trick but maintenance is an opportunity for an upgrade, right? With the Ultegra 6800 already available and Ultegra 6870 looming, prices for the Ultegra 6700 Di2 upgrade kit came down in price enough that I could talk myself into justifying the expense. So, is it difficult to install? Is it worth it?

A note on buying

If you go the online route as I did, you may wonder when comparing offers if the upgrade kit is complete. A little homework is in order. This link for Shimano's technical document for dealers will help in identifying the individual components (and give help with installation as I found the included documentation lacking detail).
 http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Ultegra/UltegraDi2/6770Di2_DM_EN_v1_m56577569830770172.pdf. The upgrade kit I purchased included the following:

①デュアルコントロールレバー・・・・・・・ST-6770 × 1 (dual control levers, set F/R)
②フロントディレイラー・・・・・・・・・・・・・・FD-6770-F(直付) × 1 (FD, braze on)
③リアディレイラー・・・・・・・・・・・・・・・・・RD-6770-SS × 1 (RD, SS as in short cage)
④バッテリー・・・・・・・・・・・・・・・・・・・・・・SM-BTR1 × 1 (battery)
⑤バッテリーチャージャー・・・・・・・・・・・SM-BCR1 × 1 (battery charger)
⑥バッテリーチャージャー用ケーブル・SM-BCC1 × 1 (battery cable, in this case for Japan)
⑦エレクトリックケーブル(ﾊﾝﾄﾞﾙ周り)・・SM-EW67A-E × 1 (cables to brifters with junction)
⑧エレクトリックケーブルセット・・・・・・・・SM-JC40-M × 1 (rear - under BB - external junction)
・ﾊﾞｯﾃﾘｰﾏｳﾝﾄ SM-BMR1-L (long battery mount, under bottle cage)
・ｴﾚｸﾄﾘｯｸｹｰﾌﾞﾙ EW-SD50(950mm×1、500mm×1、300mm×2) (electric cables)
・ｺｰﾄﾞｶﾊﾞｰ(ﾌﾞﾗｯｸ) SM-EWC2(300mm×3、50mm×3) (electric cable covers)

As the front derailleur comes in braze on only, a suitable "band adapter" or braze on adapter (SM­AD67) is required and not included. If your frame does not have a braze on mount for your FD like mine, just measure the diameter of the seat tube and order the appropriate adapter. Everything else needed for the installation was included in this kit. Although not mentioned, the "required" tool for installing the cables is included and found in the box containing the cables (hey, ya never know). All of the bundled upgrade kits I have seen come in "M" or "L" lengths. Just for reference, I am about 5'6" (167 cm) and have a 49 cm frame in the Lapierre, the "M" was just about perfect for my frame. Check this Shimano tech document for how you should measure your frame to determine the correct cable length:
http://www.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50lparsys-0034-downloadFile.html/10)%20Di2%20Wire%20Kit%20Instructions.pdf. You can always buy different length cables after - they range from 150 - 1400 mm in 50 mm increments - but they cost around 20 dollars each if you can find them. Shimano says the cables can't or should not be cut. I'll leave it at that. The battery cable is country specific, cables for outlets to match other countries are available if needed (like I bought this online from another country or want to travel with my bike). The battery is external only for Di2 6770, whether you go internal cabling or external. Most of the upgrade kits I have seen do not offer a choice in battery mounts. There is a short mount for Di2 ready frames (SM­BMR1­S). As my frame is somewhat small to begin with and this model Lapierre has "compact geometry", I did need to move the bottle cage on my seat tube up a little to accommodate the battery. If this is you, you might need the "bottle cage adapter" (SM­BA01). This is not included. I have seen bundles that do not include the wire covers for the external wiring kits (SM­EWC2). You get 3 long and 3 short (see above for length). I only used half of them for the installation on my bike. Nothing worse than starting a project and finding something missing. I spent a lot of time to figure out just what I needed. Hope this clears things up a little. With this part out of the way, onto the installation.