Dialects/Topolects: Tone Marks?
You could look at Tianjin, as close as 120 km from Beijing. The local Tianjin dialect is still exhibiting rather drastic changes to tones and tone changes.

Drawing from your example, mandarin in Beijing and Tianjin differ in tones according to the following, with TJ accent being much more low-pitched:


1st tone = 55 (BJ), 21 (TJ)
2nd tone = 35
3rd tone = 214 (BJ), 113 (TJ)
4th tone = 51 (BJ), 53 (TJ)


You also have different sandhi rules for tonal changes. Tianjin itself is pronounced Tian3jin1 in TJ. Tone marks, however, would still be identical (just as "pen" is not rendered "pin" in Texas).

This pattern repeats itself wherever you go in China. For example, the standard Wu topolect as spoken in Shanghai has differences already within the city suburbs, such as Jiading, and much more so in neighboring cities like Jiaxing, and further more in relatively remote locations such as Hangzhou and Suzhou.

From this we conclude that the standard mandarin (普通话) is merely an ideal, a common framework for speakers of countless topolects and dialects.